Prenatal care: Initial assessment

INTRODUCTION — The three main components of prenatal care are: risk assessment, health promotion and education, and therapeutic intervention [1]. High-quality prenatal care can prevent or lead to timely recognition and treatment of maternal and fetal complications. Complications of pregnancy and childbirth are the leading cause of morbidity and mortality in females of reproductive age globally [2].

This topic will discuss the initial prenatal assessment (which may require more than one visit) in the United States. Most of these issues are common to pregnancies worldwide. Preconception care, ongoing prenatal care after the initial prenatal assessment, and issues related to patient counseling are reviewed separately.

●(See "The preconception office visit".)

●(See "Prenatal care: Second and third trimesters".)

●(See "Prenatal care: Patient education, health promotion, and safety of commonly used drugs".)

●(See "COVID-19: Overview of pregnancy issues".)

GOALS — The major goal of prenatal care is to help ensure the birth of a healthy newborn while minimizing maternal risk. There are several components involved in achieving this objective:

●Early, accurate estimation of gestational age

●Identification of pregnancies at increased risk for maternal, fetal, or subsequent pediatric morbidity and mortality

●Ongoing evaluation of maternal and fetal health status

●Anticipation of problems, with intervention (if possible) to prevent or minimize morbidity

●Health promotion, education, support, and shared decision-making

●Recognition of the impact of social and structural determinants of health and disparities in health care on pregnancy outcome

●Provision of respectful maternity care

Healthy pregnant people have described the following factors as those that matter most to them for a positive pregnancy experience [3]:

●Maintaining physical, social, and cultural normality

●Maintaining a healthy pregnancy, with appropriate intervention when indicated

●When labor begins, effectively transitioning to a positive labor and birth experience

●Achieving a positive mothering experience (eg, building self-esteem, competence, and autonomy)

The World Health Organization developed 39 recommendations on antenatal care for a positive pregnancy experience. The recommendations related to five types of interventions: nutritional interventions, maternal and fetal assessment, preventive measures, interventions for common physiological symptoms, and health system interventions to improve utilization and quality of antenatal care.

EFFECTIVENESS — There is evidence that prenatal care confers some health benefits, although how it does so and the types and magnitude of benefits appear to be complex and multifactorial [4,5]. Prenatal care has many components, including timing of initiation of care, number and spacing of visits, type and quality of content (eg, assessment of risk, conditions screened for, patient education/counseling), clinical provider type/training, setting for provision of prenatal care, ancillary services (eg, nutrition, management of substance use, psychosocial support services, economic support), and prenatal care systems issues [6]. The effectiveness of many of these components or packages of components generally has not been rigorously evaluated.

The following examples are findings from meta-analyses of randomized trials of one or more components of prenatal care:

●Special assistance/support versus standard care – Special assistance may include emotional support, tangible support (eg, direct assistance, home visits), and informational support. A meta-analysis of randomized trials found that programs offering special assistance for pregnant people at risk for giving birth to a low birth weight (LBW) infant may have favorable effects compared with routine prenatal care, but the confidence intervals suggest that a true effect, if present, would not be large [7]:

•Birth weight less than 2500 g (120 out of 1000 versus 127 out of 1000 with routine care, risk ratio [RR] 0.94, 95% CI 0.86-1.04, 16 studies, >11,000 participants, moderate-quality evidence)

•Birth <37 weeks of gestation (117 out of 1000 versus 128 out of 1000 with routine care, RR 0.92, 95% CI 0.84-1.01, 14 studies, >12,000 participants, moderate-quality evidence)

Postnatal depression also appeared to be reduced slightly in the special assistance group, but meta-analysis could not be performed because of differences in reported outcomes. The risks for stillbirth and neonatal death were similar for both groups.

●Reduced versus standard number of prenatal visits – The number of visits for standard prenatal care varies among countries; therefore, what constitutes a reduced number of visits also varies. In a meta-analysis of trials of provision of prenatal care for low-risk pregnancies, patients in the reduced visit group in high-income countries had 8 to 12 prenatal visits, whereas many patients in the reduced visits group in low- and middle-income country trials had fewer than five prenatal visits. Major findings of the analysis were:

•Perinatal mortality – When compared with standard care in low-risk pregnancies, reduced visits appeared to increase perinatal mortality (RR 1.14, 95% CI 1.00-1.31, five trials, >56,000 infants, moderate-quality evidence) [8].

In the subgroup analysis, for high-income countries, the number of deaths was small (32 of 5108), with no clear difference between the groups (RR 0.90, 95% CI 0.45-1.80, two trials), whereas for low- and middle-income countries, perinatal mortality was significantly higher in the reduced visits group (RR 1.15, 95% CI 1.01-1.32, three trials).

•Other outcomes

-There was no clear difference between groups for maternal death, hypertensive disorders of pregnancy, preterm birth, or small for gestational age (SGA).

-Patients in all settings were less satisfied with the reduced visits schedule and perceived the gap between visits as too long.

-Reduced visits may be associated with lower costs.

A limitation of the analysis is that the number of visits does not necessarily reflect the care provided. (See "Prenatal care: Second and third trimesters", section on 'Frequency of prenatal visits'.)

●Group versus traditional one-on-one prenatal care – In a meta-analysis of randomized trials comparing patients receiving group prenatal care with those receiving traditional one-on-one prenatal care, both groups had similar rates of [9]:

•Preterm birth (RR 0.75, 95% CI 0.57-1.00)

•LBW (RR 0.92, 95% CI 0.68-1.23)

•SGA (RR 0.92, 95% CI 0.68-1.24)

•Perinatal mortality (RR 0.63, 95% CI 0.30-1.25)

(See "Group prenatal care".)

●Specialized clinics versus standard care for patients at high risk for preterm birth – In a meta-analysis of randomized trials comparing patients who received care at a clinic to prevent the onset of preterm labor and facilitate its early identification and treatment with those who received usual care, the intervention did not significantly reduce rates of preterm birth, very preterm birth, or stillbirth [10]. There were many limitations to these data, including heterogeneity in outcome focus, target populations, study design, and specific intervention components.

●Midwifery versus other types of obstetric care – In a meta-analysis of randomized trials comparing pregnant patients assigned to midwife-led continuity models of care with those assigned to other models of care (15 trials, over 17,000 participants), patients in midwife-led continuity models of care were less likely to experience intrapartum intervention, more likely to be satisfied with their care, and had similar rates of adverse outcomes [11].

Another systematic review that compared midwife-led models of care with other models of care reported similar findings [12]. The trials included both patients at low risk of complications and those at increased risk who were not currently experiencing problems.

●Other evidence

•A summary of evidence from Cochrane systematic reviews on the effects of antenatal interventions for preventing stillbirth for low-risk or unselected pregnancies concluded that, while most interventions were unable to demonstrate a clear effect in reducing stillbirth or perinatal death, the following interventions were beneficial: balanced energy/protein supplements, midwife-led models of care, training versus not training traditional birth attendants, and antenatal cardiotocography [13].

Possible benefits were observed for insecticide-treated antimalarial nets and community-based intervention packages, whereas a reduced number of antenatal care visits was harmful.

There was variation in the effectiveness of interventions across different settings, highlighting the importance of assessing the context in which these interventions were tested.

•Systematic reviews have supported the benefits of screening for and management of several conditions, including but not limited to: gestational diabetes mellitus, maternal Group B Streptococcus colonization, maternal RhD antigen and antibody status. (See "Gestational diabetes mellitus: Screening, diagnosis, and prevention" and "Prevention of early-onset group B streptococcal disease in neonates" and "RhD alloimmunization in pregnancy: Overview".)

In addition, frequently monitoring blood pressure in the second half of pregnancy is essential for timely diagnosis and management of preeclampsia. (See "Preeclampsia: Clinical features and diagnosis" and "Preeclampsia: Antepartum management and timing of delivery".)

•Respectful maternity care is variably defined but broadly involves absence of disrespectful conduct toward the pregnant individual (eg, physical/verbal/sexual abuse, lack of confidentiality, unnecessary examinations/procedures, discrimination, neglect/abandonment, poor communication, physical constraints) and promotion of respectful conduct (eg, informed consent/shared decision-making; dignity, respect, and privacy in interactions; equitable care; quality care; safe environment). A systematic review found that validated tools to measure respectful maternity care were available but the optimal tool was unclear [14]. Furthermore, no high-quality studies have evaluated the effectiveness of respectful maternity care for improving any maternal or infant health outcome.

TIMING — Prenatal care should be initiated in the first trimester, ideally by 10 weeks of gestation since some prenatal screening and diagnostic tests can be performed at 10 to 11 weeks of gestation. Early initiation of care is also useful to establish gestational age and early baseline maternal measurements (eg, weight [body mass index], blood pressure, laboratory evaluation [in patients with chronic diseases]) and provide early social service support and intervention, when warranted.

The percentage of pregnant patients who initiate prenatal care in the first trimester is one of the standard clinical performance measures used to assess the quality of maternal health care. In the United States, approximately 57 percent of federally funded community health centers met the Healthy People 2020 baseline for patients initiating prenatal care in the first trimester (78 percent), and only 38 percent met the Healthy People 2020 target (85 percent) [15]. The World Health Organization (WHO) estimated that 60 percent of pregnant people worldwide initiated prenatal care before 12 weeks of gestation; however, regional and income disparities were identified [16]. Less than 50 percent of pregnant people in resource-limited regions received early antenatal care versus over 80 percent in resource-abundant regions; more than 80 percent of pregnant people in the highest income group received early antenatal care versus 25 percent of those in the lowest income group.

CARE PROVIDER

●Standard one-on-one care – Prenatal care is generally provided by midwives, obstetrician-gynecologists, family medicine physicians, and/or maternal-fetal medicine (MFM) subspecialists. Midwives and family medicine physicians generally provide prenatal care for patients with pregnancies in which major complications are not anticipated. Obstetrician-gynecologists are specialists who provide prenatal care for uncomplicated and some complicated pregnancies. MFM clinicians are subspecialist obstetrician-gynecologists with expertise for managing high-risk, complicated pregnancies.

Midwifery-led care and collaboration between midwives and physicians are common models of prenatal care, influenced by the medical/obstetric needs and personal preferences of the pregnant person as well as local licensing regulations. (See 'Effectiveness' above.)

Prenatal doulas and prenatal educators are ancillary providers who provide education and support. Prenatal educators tend to deliver information in a group setting. Prenatal doulas work one-on-one with their patient and may serve as a coach. Birth doulas provide education, support, and advocacy during childbirth (see "Continuous labor support by a doula"). Postpartum and breastfeeding doulas also exist.

●Group prenatal care – Group prenatal care is an alternative means of providing prenatal care in which participants with the same month of expected delivery receive the majority of their care in a group setting. The only private times between patient and clinician are during the initial prenatal assessment, when health concerns involving need for privacy arise, and during cervical assessment late in pregnancy. The majority of the visit, which may last two hours, involves facilitated group discussion, education, and skills building to address explicit learning objectives in prenatal care, childbirth preparation, and postpartum and parenting roles.

Group prenatal care appears to result in at least equivalent obstetric outcomes and high levels of patient satisfaction compared with traditional prenatal care. (See "Group prenatal care".)

●Subspecialty obstetric care – MFM subspecialists are obstetrician-gynecologists with additional training in the area of high-risk, complicated pregnancies. A high-risk pregnancy has been defined as one in which the mother, fetus, or newborn is at risk of death or residual injury and thus requires additional resources, procedures, or specialized care to optimize outcome [17,18].

Referral to an MFM subspecialist is appropriate for individuals with chronic health conditions or serious acute disorders, those who have experienced pregnancy complications in the past, and those who develop complications during their current pregnancy; this decision depends on the obstetrician-gynecologist's level of expertise with the specific problem.

Subspecialist care for high-risk pregnancies has not been studied extensively, except for specialty clinics that provide a prenatal care package for patients at high risk of preterm birth. (See 'Effectiveness' above.)

●Multidisciplinary care – Pregnant patients with medical comorbidities benefit from collaborative multidisciplinary care by a team that includes their obstetric provider and appropriate medical or surgical subspecialists, and possibly specialists in genetics, anesthesia, and pediatrics.

COMPONENTS OF THE INITIAL PRENATAL VISIT — Appropriate historical information, physical examination, and laboratory evaluation can help identify pregnant people at increased risk of medical complications, pregnancy complications, or fetal abnormalities. Early identification of these patients gives the provider an opportunity to discuss these issues and their management with the patient and, in some cases, offer interventions to prevent or minimize the risk of an adverse outcome. Time constraints are an ongoing challenge [19,20].

History

●Medical/obstetric history – At or prior to the first prenatal visit, it is efficient for the patient to complete a questionnaire detailing their psychosocial, medical, obstetric, and family history. This information can be used to start an obstetric record that will document their prenatal, intrapartum, and postpartum course. Several paper and computerized obstetric record forms are available for this purpose. They help to ensure complete and systematic documentation of the pregnancy and often may be used for risk-assessment planning.

The major elements of the patient history include:

•Demographic information (including age, education/health literacy, occupation, race/ethnicity, religious concerns regarding blood transfusion and information about the patient's partner) (see "Approach to the patient who declines blood transfusion").

•Past obstetric history (table 1).

-If the patient has risk factors for ectopic pregnancy (table 2), early identification of the location of the pregnancy is important. (See "Ectopic pregnancy: Epidemiology, risk factors, and anatomic sites", section on 'Risk factors' and "Ectopic pregnancy: Clinical manifestations and diagnosis", section on 'Diagnostic evaluation' and "Approach to the patient with pregnancy of unknown location".)

-An adverse outcome in a previous pregnancy increases the risk of an adverse outcome in the next pregnancy. (See "Spontaneous preterm birth: Overview of risk factors and prognosis" and "Stillbirth: Incidence, risk factors, etiology, and prevention" and "Fetal growth restriction: Evaluation" and "Acute placental abruption: Management and long-term prognosis".)

•Personal medical history, including allergies, medications (prescription and nonprescription), and immunizations; risk assessment for heritable disorders and substance use (illicit drugs, recreational drugs, nonmedical use of medications, alcohol); infection history/exposure; and toxic exposures in the workplace, home, or recreational activities (table 3).

In particular:

-Clinicians need to be attentive to the signs and symptoms of heart disease (fatigue, palpitation, dyspnea, or anginal pain), particularly in patients with risk factors, as failure to identify an underlying heart condition, failure to recognize a high-risk patient, delay in treatment or intervention, and late recognition of cardiac deterioration substantially contribute to the occurrence of serious cardiac events in pregnancy [21]. (See "Acquired heart disease and pregnancy" and "Pregnancy in women with congenital heart disease: General principles".)

-Use of validated screening tool for substance use is recommended (table 4). Screen-positive patients should be appropriately evaluated and treated. (See "Substance use during pregnancy: Screening and prenatal care", section on 'Screening for substance use' and "Substance use during pregnancy: Screening and prenatal care", section on 'Prenatal care of individuals with substance use disorder'.)

-Although rare, patients should be queried about a history of phenylketonuria, which is detected on newborn screening. If the patient does not volunteer the diagnosis because they are no longer on a restricted diet, asking about dietary restrictions during childhood might reveal the diagnosis. Elevated serum phenylalanine concentration during early pregnancy in a mother with phenylketonuria or hyperphenylalaninemia can result in phenylalanine embryopathy, which can be prevented by dietary restriction of phenylalanine intake. (See "Overview of phenylketonuria".)

•Family medical history (a tool is available online).

-Findings in the family history that may suggest a heritable disorder impacting the fetus include known or suspected genetic disease, multiple malformations, multiple miscarriages, recurrence of the same or similar disorders, intellectual disability, autism spectrum disorder, and consanguinity.

•Past surgical history, including bariatric surgery. (See "Fertility and pregnancy after bariatric surgery".)

•Menstrual and gynecologic history. (See "The gynecologic history and pelvic examination".)

•Current pregnancy history, including the patient's desire for the pregnancy.

•Potential exposure to infection (eg, malaria, tuberculosis, Zika virus, Chagas disease) because of travel.

•Exposure to potentially toxic environmental agents (table 3), including (see "Occupational and environmental risks to reproduction in females: Specific exposures and impact" and "Overview of occupational and environmental risks to reproduction in females" and "Diagnostic imaging in pregnant and lactating patients"):

-Antineoplastic drugs

-Air pollutants, including cigarette smoke

-Heavy metals (lead, mercury, cadmium)

-Radiation

-Chemicals (eg, ethylene oxide, formaldehyde, flame retardants, solvents, perfluorochemicals, pesticides, endocrine-disrupting chemicals [bisphenol A, phthalates, polybrominated diethyl ethers])

●Psychosocial history – Psychosocial issues of potential concern that should be identified and discussed with the patient include [22,23]:

•Planned or unintended pregnancy.

•Potential barriers to care (eg, cognitive impairment, physical disability, language and other communication issues, lack of transportation, lack of childcare, economic constraints, work schedule, legal/immigration status, emotional stress/ family or personal problems/depression, negative perceptions or fear of health care providers or services).

•Mental health and level of stress (including depression screening, access to interpersonal support, self-esteem/agency issues). The American College of Obstetricians and Gynecologists (ACOG) suggests screening patients for depression and anxiety at the initial prenatal visit, later in pregnancy, and at postpartum visits using a standardized, validated tool, such as the PHQ-9 or Edinburgh Postnatal Depression Scale (table 5 and figure 1A-B) [23]. Other tools are available, such as the PHQ-4, which screens for both anxiety and depression (table 6), and the GAD-7 scale (table 7), which assesses severity of anxiety. Practices may distribute questionnaires at check-in for patients to complete or have staff distribute or verbally administer questionnaires along with measuring vital signs. The provider can further evaluate patients who screen positive. Systems should be in place to ensure timely access to assessment and diagnosis, effective treatment, and appropriate monitoring and follow-up based on severity.

If pharmacotherapy for depression is initiated, screening for bipolar disorder (table 8) should be performed first because misdiagnosis can lead to an inappropriate choice of depression treatment, which may precipitate mania, psychosis, or mixed states. A state-based Perinatal Psychiatry Access Program is a useful resource for managing patients with mental health conditions [24]. (See "Unipolar major depression during pregnancy: Epidemiology, clinical features, assessment, and diagnosis" and "Generalized anxiety disorder in adults: Epidemiology, pathogenesis, clinical manifestations, course, assessment, and diagnosis" and "Bipolar disorder in adults: Assessment and diagnosis" and "Bipolar major depression in adults: Choosing treatment" and "Bipolar mania and hypomania in adults: Choosing pharmacotherapy" and "Bipolar disorder in postpartum women: Epidemiology, clinical features, assessment, and diagnosis".)

•Presence/absence of stable housing and food security.

•Victim of violence (past history and future risk) – Clinicians should routinely assess all pregnant patients for past or current exposure to interpersonal violence [25-27]. Markers and characteristics of abuse include bruising, improbable injury, depression, late prenatal care (presentation in the late second or the third trimester), missed prenatal visits, and appointments cancelled on short notice.

Exposure to intimate partner violence is associated with an increased risk of low birth weight (LBW) newborns and preterm birth [28]. In the United States, homicide during pregnancy or within 42 days postpartum exceeds maternal mortality from hemorrhage, hypertensive disorders, or infection [29]. Counseling and intervention can reduce intimate partner violence and improve pregnancy outcome [30]. (See "Intimate partner violence: Epidemiology and health consequences", section on 'Pregnancy' and "Intimate partner violence: Diagnosis and screening" and "Intimate partner violence: Intervention and patient management".)

Patients with past histories of sexual trauma may have psychological distress triggered by the normal process of prenatal care, labor, and delivery; discussion of these issues with the patient and modifications in some aspects of care may alleviate some of this distress (table 9) [31,32]. Health care issues specific to female patients with trauma exposure, challenges in providing prenatal care, and techniques to reduce retraumatization (ie, trauma-informed care) are discussed in detail separately. (See "Health care for female trauma survivors (with posttraumatic stress disorder or similarly severe symptoms)".)

•Status of previous children (eg, living with the parent and/or partner, foster care, adoption)

Calculating the estimated date of delivery — Calculators are available for determining the estimated date of delivery (EDD) and gestational age (calculator 1 and calculator 2) from the date of the last menstrual period. Accurate dating is crucial for managing the pregnancy, especially with regard to timing interventions and monitoring fetal growth. Sonographic estimation of the EDD before 20 weeks of gestation is desirable in all pregnancies. (See 'Ultrasound examination' below.)

Physical examination — Baseline blood pressure [33,34], weight, and height should be recorded. Calculating body mass index (calculator 3) facilitates counseling about the appropriate amount of weight gain over the course of pregnancy (table 10). Patients who are underweight or have obesity are counseled about their specific risks in pregnancy. (See "Gestational weight gain" and "Obesity in pregnancy: Complications and maternal management".)

If the initial blood pressure is elevated, the clinician should attempt to find records of prepregnancy blood pressures to document whether the patient has chronic (preexisting) hypertension (ie, elevated blood pressure: systolic 120 to 129 mmHg and diastolic <80 mmHg, stage 1 hypertension: systolic 130 to 139 mmHg or diastolic 80 to 89 mmHg, stage 2 hypertension: systolic ≥140 mmHg or diastolic ≥90 mmHg). This information can be important in establishing the correct diagnosis (chronic hypertension versus preeclampsia versus gestational hypertension) if blood pressure increases in the second half of pregnancy. If blood pressure is measured using an automated device, it should have been properly validated in a pregnant population [35]. Management of chronic hypertension in pregnancy is discussed separately. (See "Chronic hypertension in pregnancy: Prenatal and postpartum care".)

A complete physical examination is performed, with special attention to uterine size and shape and evaluation of the adnexa. The size-gestational age correlation is learned by experience and is often described in terms of fruit (eg, for singleton pregnancies: 6 to 8 week size = plum, 8 to 10 week size = orange, 10 to 12 week size = grapefruit), despite the imprecision of this terminology. When the uterine size on physical examination differs from that predicted by menstrual dating, early sonographic assessment is indicated. Causes for a discrepancy between the actual uterine size and that predicted by the last menstrual period include uterine fibroids, uterine malposition (eg, retroverted uterus), multiple gestation, and incorrect last menstrual date. (See "Prenatal assessment of gestational age, date of delivery, and fetal weight" and "Uterine fibroids (leiomyomas): Issues in pregnancy".)

When fetal heart activity is present, the fetal heart can usually be heard by 12 weeks of gestation using a hand-held Doppler ultrasound device. Transvaginal ultrasound scanners can identify fetal cardiac motion as early as 5.5 weeks.

Ultrasound examination

●Gestational age – Ultrasound examination in the first trimester to determine gestational age is particularly important when menses are irregular, the last menstrual period is unknown or uncertain, in patients who conceive while using hormonal contraception, and when the uterine size is discordant with menstrual dates. Routine early (before 20 weeks of gestation) ultrasound examination provides a better estimation of gestational age than menstrual dates, resulting in significant reductions in the frequency of labor induction for postterm pregnancy and tocolysis for suspected preterm labor. More accurate estimation of EDD may also reduce planned cesarean birth before 39 weeks of gestation resulting from misdiagnosis of gestational age. These data are reviewed separately. (See "Prenatal assessment of gestational age, date of delivery, and fetal weight".)

The assessment of appropriate fetal/neonatal size is based upon the expected weight for gestational age. If gestational age is overestimated, then an appropriately grown fetus/neonate may be incorrectly classified as growth restricted or small for gestational age (SGA) and receive inappropriate intervention. However, in a 2015 Cochrane review of trials of routine/revealed ultrasound versus selective/concealed ultrasound before the 24^th week of pregnancy, routine use of early ultrasound did not result in a significant reduction in diagnosis of SGA (relative risk 1.05, 95% CI 0.81-1.35; three trials, >17,000 pregnancies) [36].

●Multiple gestation – First-trimester ultrasound examination can lead to early detection of a multiple gestation and determination of chorionicity and amnionicity. (See "Twin pregnancy: Overview", section on 'Sonographic diagnostic evaluation'.)

●Congenital anomalies – First-trimester ultrasound examination can lead to early detection of fetal anomalies and anatomic markers associated with common aneuploidies [36-38]. (See 'Aneuploidy screening and diagnosis' below and 'Fetal anomaly screening' below.)

Discussion of screening and diagnostic testing for genetic and anatomic abnormalities — Patients undergoing any screening test should understand the difference between a screening test and diagnostic test. This is particularly important in genetic screening, in which couples need to understand what is and is not being screened for, the interpretation of screen-positive and -negative results, the possibility of false-positive and -negative results, possible follow-up invasive or noninvasive testing, and possible reproductive choices.

Aneuploidy screening and diagnosis — We believe that all pregnant patients should be offered prenatal genetic screening (serum biomarker screening with or without nuchal translucency or cell-free DNA screening) and should have the option of having an invasive procedure for diagnostic testing instead of noninvasive screening (regardless of maternal age), in agreement with ACOG guidance [39].

Diagnostic testing involves performing genetic studies on samples (eg, chorionic villi or amniocytes) obtained by an invasive procedure, typically chorionic villus biopsy or amniocentesis, to identify fetuses who are aneuploid. (See "Chorionic villus sampling" and "Diagnostic amniocentesis".)

Screening tests identify fetuses at high risk of aneuploidy and fall into two major categories:

●Assessment of cell-free DNA in the maternal circulation to screen for trisomy 21, trisomy 18, trisomy 13, and sex chromosome aneuploidies is an increasingly popular option. (See "Prenatal screening for common aneuploidies using cell-free DNA".)

●Assessment of maternal serum levels of specific biochemical markers associated with trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome), with or without assessment of specific ultrasound markers, is another option. This approach may lead to detection of fetal conditions beyond the primary targets. (See "Down syndrome: Overview of prenatal screening", section on 'Tests integrated across the first and second trimesters' and "Down syndrome: Overview of prenatal screening", section on 'First-trimester combined test' and "Down syndrome: Overview of prenatal screening", section on 'Second-trimester quadruple test'.)

Either approach is acceptable if the patient receives appropriate pretest genetic counseling to make an informed choice, including no screening or testing. The cost can differ substantially depending on the approach and is another factor for the patient to consider.

Fetal anomaly screening — Increasingly, a first-trimester fetal anatomy scan is performed before, in conjunction with, or after first-trimester aneuploidy screening. Detection of fetal anomalies in the first trimester is limited by small fetal size, ongoing fetal development, and maternal habitus. Nevertheless, ultrasound technology is rapidly progressing and assessment of fetal anatomy in the first trimester is becoming more widely available. In a 2017 systematic review of 30 studies from 1991 to 2014, the sensitivity of first-trimester ultrasound screening for detection of fetal anomalies in low-risk or unselected populations was 32 percent (95% CI 22-43 percent) and, in high-risk populations, 61 percent (95% CI 38-82 percent) [37]. When only major anomalies were considered, sensitivity in low-risk or unselected populations was 46 percent. An anomaly of any type was present in 1.8 in 100 fetuses in low-risk pregnancies and 6.6 in 100 fetuses in high-risk pregnancies; a major anomaly was present in 1 in 100 fetuses in low-risk pregnancies. No information was available on specific anomalies. Although there was considerable heterogeneity among these studies and sonographic equipment and expertise improved over the 23-year study period and since the study was done, the findings affirm both the potential benefits and limitations of the first-trimester fetal anatomic survey. Most patients will need a second-trimester survey to provide a more reliable assessment of fetal anatomy.

The type and order of testing depend on patient preference, which is often influenced by insurance coverage. As an example, for patients who elect genetic screening rather than testing, many will have an ultrasound at 10 to 13 weeks to confirm gestational age and fetal heart activity, determine the number of fetuses, assess for aneuploidy markers such as enlarged nuchal translucency, and evaluate early fetal anatomy, acknowledging that early fetal anatomy is best evaluated at the latter part of this interval (12 to 13 weeks). Blood for cell-free DNA screening is often drawn at this visit; however, patients with enlarged nuchal translucency or multiple soft markers may opt for diagnostic testing instead of screening based on the sonographic findings. If the ultrasound is normal, the patient returns at 18 to 20 weeks for a detailed anatomy scan. For patients who opt for diagnostic testing rather than screening, chorionic villus sampling (CVS) can be performed at the 10 to 13 weeks ultrasound examination. For the rare patient who prefers an amniocentesis to CVS, we suggest an ultrasound at 10 to 13 weeks to assess for indications for earlier genetic testing (eg, enlarged nuchal translucency) and if none are found, the patient is reassured that waiting until 15 to 16 weeks for the amniocentesis is reasonable. (See "Prenatal genetic evaluation of the fetus with anomalies or soft markers", section on 'Approach to the evaluation of the fetus with "soft markers" and no structural anomalies'.)

Carrier screening — In the United States, genetic carrier screening for cystic fibrosis and spinal muscular atrophy is offered routinely and, at a minimum, red blood cell indices are routinely used to screen for carriers of hemoglobinopathies [40]; however, we prefer the addition of high performance liquid chromatography or capillary electrophoresis, as shown in the algorithm (algorithm 1). (See "Hemoglobinopathy: Screening and counseling in the reproductive setting and fetal diagnosis".)

For other heritable disorders, clinicians may choose to take an ethnic-specific or panethnic approach. Alternatively, clinicians may offer all patients an expanded carrier screening panel. (See "Preconception and prenatal panethnic expanded carrier screening".)

If the patient is found to be a carrier for a specific condition, their reproductive partner should be offered screening to determine the risk of an affected child. Referral to a genetic counselor is useful to discuss the specific disorder, residual risk, options for prenatal diagnosis, and the patient's reproductive options. One study found that the most common missed indications for genetics referral were personal or family history of congenital anomalies, intellectual disability, autism, and positive genetic carrier screening test [41]. (See "Genetic counseling: Family history interpretation and risk assessment".)

Information on specific disorders is available separately, including but not limited to:

●Cystic fibrosis. (See "Cystic fibrosis: Carrier screening".)

●Spinal muscular atrophy. (See "Spinal muscular atrophy", section on 'Genetics'.)

●Hemoglobinopathy (eg, alpha or beta thalassemia; hemoglobin S, C, D, or E) – (See "Hemoglobinopathy: Screening and counseling in the reproductive setting and fetal diagnosis".)

●Fragile X syndrome. (See "Fragile X syndrome: Prenatal screening and diagnosis", section on 'Screening'.)

●Disorders such as Tay-Sachs disease, Canavan disease, cystic fibrosis, familial dysautonomia, mucolipidosis IV, Niemann Pick disease type A, Fanconi anemia group C, Bloom syndrome, Gaucher disease, familial hyperinsulinism, glycogen storage disease type I, Joubert syndrome, maple syrup urine disease, and Usher syndrome are more common in people of Ashkenazi Jewish ancestry.

Tay-Sachs disease is also more common among people of Pennsylvania Dutch, Southern Louisiana Cajun, and Eastern Quebec French Canadian ancestry. (See "Preconception and prenatal carrier screening for genetic disorders more common in people of Ashkenazi Jewish descent and others with a family history of these disorders".)

●Skeletal dysplasia. (See "Approach to prenatal diagnosis of the lethal (life-limiting) skeletal dysplasias" and "Skeletal dysplasias: Specific disorders".)

Genome-wide fetal screening — The clinical utility of expanding cell-free DNA testing of maternal blood to include panels of microdeletions and microduplications, rare autosomal trisomies, and monogenic disorders has not been established. Professional societies, such as the American College of Medical Genetics and Genomics, European and American Societies for Human Genetics, Society for Maternal-Fetal Medicine (SMFM), and International Society for Prenatal Diagnosis, recommend against offering expanded cell-free DNA testing as part of routine prenatal genetic screening, while endorsing its use for screening for trisomies 21, 18, and 13 and sex chromosome aneuploidy [42-44]. Patients who desire to maximize information about the genetic status of their fetus should undergo diagnostic testing of amniocytes or chorionic villi by microarray. The potential for detecting a microdeletion/microduplication by microarray is 30- to 50-fold greater than that by cell-free DNA screening of maternal blood [45].

The recommendation against expanded cell-free DNA screening was made because it is not possible to provide reliable estimates of no call rates, detection rates, false-positive rates, or positive predictive values, given the small numbers of cases detected, variable penetrance, uncertainty in the underlying prevalence, difficulty in follow-up, and lack of clinical validation based on real samples. Expanded noninvasive genetic screening using cell-free DNA is discussed in detail separately. (See "Cell-free DNA screening for fetal conditions other than the common aneuploidies".)

Issues related to consanguinity — Consanguinity, which is defined as the reproductive union of second cousins or closer relatives, is common in several ethnic/religious groups and increases the fetal risk for recessive disorders due to runs of homozygosity, including inborn errors of metabolism, common variable immune deficiency, some types of deafness, and congenital abnormalities with a complex etiology [46,47]. It is most common in North Africa and parts of sub-Saharan Africa, the Middle East, and west, central, and south Asia (eg, Pakistan, India), but consanguineous couples can be found anywhere because of local customs and immigration; thus, it is prudent to assess the possibility of consanguinity in all pregnant couples [48].

Consanguineous couples should be offered genetic counseling to discuss the increased risk of recessive conditions in their offspring, as well as increased risks for stillbirth or perinatal mortality. First cousins share approximately one-eighth of their variants. For a variant with a frequency of 1 in 100, the chance that unrelated partners will both be carriers of the pathogenic variant is 1/100 X 1/100 = 1/10,000, whereas the chance that two first cousins will both be carriers is 1/100 X 1/8 = 1/800 [49]. The prevalence of congenital disorders in the offspring of first cousins has been estimated to be 1.7 to 2.8 percent higher than the background population risk, mostly attributable to autosomal recessive diseases [50].

Laboratory tests

Confirmation of pregnancy — In the absence of diagnostic physical findings of pregnancy (ie, an ultrasound image of the gestational sac/embryo/fetus or auscultation of fetal heart activity by a hand-held Doppler device), suspected pregnancy should be confirmed by detection of the beta-subunit of human chorionic gonadotropin (hCG) in blood or urine. (See "Clinical manifestations and diagnosis of early pregnancy", section on 'Diagnosis'.)

Standard panel — A standard panel of laboratory tests is obtained on every pregnant patient at the first prenatal visit, augmented by additional tests in those at risk for specific conditions (see 'Selective screening' below). Repetition of tests performed preconceptionally is unnecessary.

We perform the following assessments, which are generally consistent with recommendations from ACOG [51]. The rationale for each test and implications of findings are also addressed.

ABO and RhD type and antibody screen — RhD-negative pregnant people without alloantibodies should receive prophylactic anti(D)-immune globulin at 28 weeks of gestation (or at 28 and 34 weeks in some countries) and when clinically indicated to prevent alloimmunization. (See "RhD alloimmunization: Prevention in pregnant and postpartum patients", section on 'Guidelines for prevention of anti-D alloimmunization (United States)'.)

RhD-positive or -negative pregnant people who have a positive antibody screen may be at risk for hemolytic disease of the fetus and newborn. Evaluation and management of these pregnancies are reviewed separately. (See "RhD alloimmunization in pregnancy: Overview" and "RhD alloimmunization in pregnancy: Management" and "Management of non-RhD red blood cell alloantibodies during pregnancy".)

Hematocrit or hemoglobin, mean corpuscular volume, ferritin — Anemia is generally defined by a hemoglobin level <11 g/dL (hematocrit <33 percent) in the first and third trimester and <10.5 g/dL (approximate hematocrit <32 percent) in the second trimester [52]. It is commonly related to iron deficiency. Increasingly, pregnant patients are screened for iron deficiency with a ferritin level, even when not anemic. This is based on the concern that limiting testing to those with anemia or a low mean corpuscular volume (MCV) has the potential to miss a substantial number of iron-deficient patients and deprive them of a straightforward therapy (oral or intravenous iron replacement) that is potentially beneficial to both the mother and the child and is not harmful. (See "Anemia in pregnancy".)

An MCV <80 fL in the absence of iron deficiency suggests thalassemia; further testing with hemoglobin electrophoresis is indicated. (See "Hemoglobinopathy: Screening and counseling in the reproductive setting and fetal diagnosis".)

Documentation of rubella immunity — Serologic screening for rubella immunity is performed unless the patient is known to be immune by previous serologic testing. Once documentation of immunity to rubella as a result of infection or immunization has been obtained, repeat testing is unnecessary.

If nonimmune, the patient should be counseled to avoid exposure to individuals with rubella and receive postpartum immunization. The rubella vaccine is a live vaccine and thus contraindicated during pregnancy. (See "Immunizations during pregnancy", section on 'Measles, mumps, rubella'.)

Documentation of varicella immunity — Immunity to varicella is based on a health care provider's diagnosis of varicella or verification of history of varicella disease, documented vaccination, or laboratory evidence of immunity (note: post-vaccination serology is not recommended for any recipients of varicella vaccine, including health care personnel. Commercially available antibody assays are not sufficiently sensitive to reliably detect vaccine-induced antibody, which may result in false-negative results and unnecessary revaccination).

Pregnant people who do not have evidence of immunity to varicella should be counseled to avoid exposure to individuals with varicella, may be candidates for passive immunization during pregnancy if exposed to varicella, and are candidates for varicella vaccination postpartum [53]. The varicella vaccine is a live vaccine and thus contraindicated during pregnancy. (See "Immunizations during pregnancy", section on 'Varicella'.)

Urine protein — Screening for proteinuria, such as with a dipstick, is useful as a baseline for comparison with testing performed later in pregnancy. (See "Proteinuria in pregnancy: Diagnosis, differential diagnosis, and management of nephrotic syndrome" and "Preeclampsia: Clinical features and diagnosis".)

Urine culture — Routine urine culture in early pregnancy is recommended because untreated asymptomatic bacteriuria places the patient at high risk of developing pyelonephritis and at modestly increased risk for preterm birth; rapid tests for bacteriuria do not have adequate sensitivity and specificity. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy", section on 'Diagnosis'.)

Treatment of a positive culture is per standard guidelines; however, some clinicians treat group B streptococcal (GBS) bacteriuria at colony counts <10⁵ CFU/mL. Presence of GBS bacteriuria at any colony count is an indication for intrapartum GBS prophylaxis to prevent early-onset neonatal infection. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy", section on 'Management' and "Group B streptococcal infection in pregnant individuals", section on 'Asymptomatic bacteriuria'.)

Up to 30 percent of pregnant patients fail to clear asymptomatic bacteriuria following a short course of therapy [54]. Thus, a repeat culture is generally recommended as a test of cure, which can be performed a week after completion of therapy for asymptomatic bacteriuria [55]. However, there are insufficient data informing the utility of repeat testing following an initial episode of asymptomatic bacteriuria, and it is not known whether retreatment of recurrent or persistent bacteriuria improves outcomes. Management, including further testing and use of suppressive or prophylactic antibiotics for persistent or recurrent asymptomatic bacteriuria, is reviewed separately. (See "Urinary tract infections and asymptomatic bacteriuria in pregnancy".)

Cervical cancer screening — The frequency of cervical cancer screening is not affected by the pregnant state, but management of an abnormal test result is different for pregnant patients. (See "Screening for cervical cancer in resource-rich settings" and "Cervical intraepithelial neoplasia: Management", section on 'Pregnant patients' and "Cervical cancer in pregnancy".)

HIV — Medical organizations generally support universal HIV testing of pregnant patients early in each pregnancy using an "opt-out" approach [56-61]. Advantages of universal testing include:

●Appropriate medical management can be initiated.

●Patients can be counseled about prevention of transmission to or identification of infected partners.

●Perinatal transmission can be substantially reduced with appropriate intervention (eg, antiretroviral therapy antepartum and intrapartum, cesarean birth, avoidance of breastfeeding). (See "Prenatal evaluation of women with HIV in resource-rich settings" and "Antiretroviral selection and management in pregnant individuals with HIV in resource-rich settings".)

●An informed decision can be made about continuing the pregnancy.

An opt-out approach can achieve high rates of testing (95 to 100 percent in some studies), whereas an opt-in policy has had testing rates of only 50 to 60 percent due to patient refusal or clinician failure to offer the test [62,63].

Local regulations may require patient notification as well as a signed consent form indicating permission for HIV testing. The medical record should document the patient's decision to accept or decline testing. Reasons for refusal should be explored and testing offered again at another time.

Risk factors for acquiring HIV and serologic testing are discussed in detail separately. (See "Screening for sexually transmitted infections".)

Syphilis — Serologic testing to diagnose syphilis should be performed and can be done with a either a nontreponemal or treponemal test, depending on the preference of the laboratory performing the test (algorithm 2). Confirmatory testing is necessary due to the potential for false-positive results with these tests. The diagnostic approach is the same as in nonpregnant individuals. The cost and morbidity associated with testing for syphilis are low and the benefits of detecting and treating the disease during pregnancy are high for both mother and child. (See "Syphilis in pregnancy".)

Hepatitis B — All pregnant patients are screened for hepatitis in each pregnancy, regardless of previous vaccination status, because prevaccination screening to exclude acute or chronic hepatitis B virus (HBV) infection is not commonly performed. The initial screen (called the triple panel) consists of hepatitis B surface antigen (HBsAg), hepatitis B surface antibody (anti-HBs), and total hepatitis B core antibody (anti-HBc). If a previous triple panel was negative and the patient has had no HBV exposures since the triple panel was performed, then subsequent screening can be limited to HBsAg testing. However, patients who are at high risk for HBV infection (eg, injection drug user, sexual partner or household contact with chronic HBV) should be tested for anti-HBs and anti-HBc as well. Patients who are susceptible to infection should be offered immunization. (See "Immunizations during pregnancy", section on 'Hepatitis B'.)

Pregnant people who carry HBsAg can transmit HBV to the fetus, typically during birth. Passive and active immunization of the newborn within 12 hours of birth can reduce the risk of HBV transmission by >95 percent. Management of screen-positive pregnant patients is shown in the algorithm (algorithm 3) and discussed in detail separately. (See "Epidemiology, transmission, and prevention of hepatitis B virus infection", section on 'Mother-to-child transmission' and "Hepatitis B and pregnancy".)

Hepatitis C — Hepatitis C virus (HCV) screening is recommended for all pregnant individuals at the first prenatal visit of each pregnancy. The rationale is that HCV infection is increasing in females of childbearing age, risk-based screening is not consistently performed, risk-based screening alone fails to detect a sizable minority of infected individuals, and documentation of infection may affect pregnancy management (eg, avoid chorionic villus sampling and use of an internal fetal heart rate monitoring electrode) [64-68]. In addition, knowledge of HCV status during pregnancy facilitates appropriate postpartum maternal treatment and informs infant follow-up.

Initial screening or diagnostic testing for chronic HCV typically begins with an antibody test by immunoassay. (See "Screening and diagnosis of chronic hepatitis C virus infection", section on 'Standard approach'.)

●If the antibody test is nonreactive, then chronic HCV infection is unlikely and testing can stop. (See "Screening and diagnosis of chronic hepatitis C virus infection", section on 'Nonreactive anti-HCV antibody'.)

●Reactive HCV antibody tests should be followed with an HCV RNA test. The absence of detectable HCV RNA using a sensitive assay essentially confirms the absence of chronic HCV infection. False-negative tests for RNA are unusual. A reactive antibody test in this setting is generally a false positive or reflective of past, cleared infection. (See "Screening and diagnosis of chronic hepatitis C virus infection", section on 'Reactive antibody and negative RNA test'.)

●A positive HCV RNA result is evidence of HCV infection. (See "Screening and diagnosis of chronic hepatitis C virus infection", section on 'Reactive antibody and positive RNA test'.)

In 2020, the CDC revised their previous risk-factor-based guidance and recommended universal HCV screening during each pregnancy, except in settings where the prevalence of HCV infection is <0.1 percent [69]. In the absence of available data for HCV prevalence, they advised health care providers to initiate universal HCV screening until they establish that the prevalence of HCV RNA positivity in their population is <0.1 percent. The same year, the USPSTF recommended one-time HCV screening for asymptomatic adults aged 18 to 79 years (including pregnant persons) without known liver disease [70]. In 2021, ACOG and the SMFM updated their hepatitis C screening guidance to recommend HCV screening for all pregnant individuals at the first prenatal visit of each pregnancy [71]. The goal is to connect pregnant patients who screen positive for HCV with appropriate care so (1) they can begin direct-acting antiviral treatment postpartum and after completion of breastfeeding and (2) the pediatrician responsible for the care of their newborn is informed about their hepatitis C carrier status.

If universal screening is not performed, risk-based screening is indicated. Several organizations have provided guidelines that describe criteria for considering an individual high risk, regardless of pregnancy status. Despite having reviewed similar data, the various guidelines are not concordant. In a study that offered screening for HCV antibody to all pregnant people presenting for prenatal care before 23 weeks of gestation, over 106,000 patients were screened, and HCV antibody seroprevalence was 2.4 cases per 1000 pregnant people (95% CI 2.1-2.7) [72]. Factors associated with HCV antibody positivity included injection drug use (adjusted odds ratio [aOR] 22.9, 95% CI 8.2-64.0), blood transfusion (aOR 3.7, 95% CI 1.3-10.4), a partner with HCV (aOR 6.3, 95% CI 1.8-22.6), more than three lifetime sexual partners (aOR 5.3, 95% CI 1.4-19.8), and smoking (aOR 2.4, 95% CI 1.2-4.6). A composite of any of these risk factors had 91 percent sensitivity for detecting HCV antibody. These findings suggest that traditional historic risk factors for HCV screening should be expanded to include more than three lifetime sexual partners and possibly smoking. (See "Epidemiology and transmission of hepatitis C virus infection" and "Screening and diagnosis of chronic hepatitis C virus infection" and "Vertical transmission of hepatitis C virus".)

Chlamydia — Chlamydia prevalence is highly related to age and sexual behavior. The Centers for Disease Control and Prevention (CDC) and United States Preventive Services Task Force (USPSTF) recommend screening all pregnant people <25 years of age and those ≥25 years of age with risk factors for sexually transmitted infection (table 11) [61,73].

Nucleic acid amplification tests (NAATs) have high sensitivity and excellent specificity for detection of Chlamydia trachomatis, and are superior to culture. During prenatal care, the preferred approach is to test a specimen obtained from a swab of the endocervix or vagina, although urine testing appears to be as sensitive [61,74-78]. Some NAATs have been cleared by the US Food and Drug Administration (FDA) for use on liquid-based cytology specimens.

Patients with positive test results should be treated. In pregnancy, they then undergo a test-of-cure three to four weeks after treatment and are retested three to four months later [61]. (See "Clinical manifestations and diagnosis of Chlamydia trachomatis infections", section on 'Nucleic acid amplification testing (test of choice)'.)

Selective screening

Thyroid function — Both hyper- and hypothyroidism during pregnancy can have adverse effects on the mother and child. (See "Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes", section on 'Pregnancy complications' and "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment", section on 'Pregnancy complications'.)

Pregnant people with signs or symptoms of thyroid disease should undergo measurement of thyroid-stimulating hormone (TSH) level. The TSH should be interpreted using population- and trimester-specific TSH reference ranges for pregnant people, when available. If the TSH is abnormal, free or total T4 should be measured.

●The diagnosis of overt hyperthyroidism during pregnancy is based primarily upon a suppressed (<0.1 milli-units/L) or undetectable (<0.01 milli-units/L) serum TSH value and a free T4 and/or free T3 (or total T4 and/or total T3) measurement that exceeds the normal range for pregnancy. (See "Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes", section on 'Diagnosis'.)

●The diagnosis of overt primary hypothyroidism during pregnancy is based upon a TSH above the population- and trimester-specific upper limit of normal, or above 4 milli-units/L when local reference ranges are not available, in conjunction with a decreased free T4 concentration (below assay normal using reference range for pregnant women). (See "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment", section on 'Diagnosis'.)

●The diagnosis of subclinical hypothyroidism during pregnancy is based upon an elevated trimester-specific serum TSH concentration and a normal free T4 concentration.

Screening for asymptomatic hypothyroidism is controversial. Professional societies (eg, ACOG [79], the Endocrine Society [80], the American Thyroid Association [81]) recommend targeted rather than universal screening in pregnancy, which is our approach. However, a targeted approach will miss as many as one-third of pregnant patients with subclinical hypothyroidism [82-85]. For this reason and concern that not treating these patients may be associated with adverse pregnancy outcomes, some experts have advocated universal screening for thyroid dysfunction in pregnancy or in patients planning to become pregnant [86]. Criteria for selecting candidates for targeted TSH screening (eg, personal or family history of thyroid disease, type 1 diabetes mellitus, or clinical suspicion of thyroid disease), diagnostic evaluation (free T4, TPO antibodies) of patients with an elevated trimester-specific serum TSH concentration, and decision-making regarding treatment of these patients are reviewed separately. (See "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment", section on 'Screening' and "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment", section on 'Effect of thyroid hormone replacement' and "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment", section on 'Indications for treatment'.)

Type 2 diabetes — Both the American Diabetes Association (ADA) and ACOG suggest early pregnancy testing for undiagnosed type 2 diabetes in patients with risk factors [87,88]. By contrast, a USPSTF guideline concluded available evidence was insufficient to assess the balance of benefits and harms of screening asymptomatic pregnant people for glucose intolerance before 24 weeks of gestation [89,90].

The ADA defines patients at increased risk of undiagnosed type 2 diabetes based on BMI ≥25 kg/m² (≥23 kg/m² in Asian Americans) plus one or more of the following [88]:

●Gestational diabetes mellitus in a previous pregnancy

●A1C ≥5.7 percent (39 mmol/mol), impaired glucose tolerance, or impaired fasting glucose on previous testing

●First-degree relative with diabetes

●High-risk race/ethnicity (eg, African American, Latin American, Native American, Asian American, Pacific Islander)

●History of cardiovascular disease

●Hypertension (≥140/90 mmHg) or on therapy for hypertension

●HDL cholesterol level <35 mg/dL (0.90 mmol/L) and/or a triglyceride level >250 mg/dL (2.82 mmol/L)

●Polycystic ovary syndrome

●Physical inactivity

●Other clinical condition associated with insulin resistance (eg, severe obesity, acanthosis nigricans)

For patients at increased risk of diabetes, a diagnosis of overt diabetes can be made at the initial prenatal visit if:

●Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) or

●A1C ≥6.5 percent (48 mmol/mol) using a standardized assay or

●Random plasma glucose ≥200 mg/dL (11.1 mmol/L) and classic symptoms of hyperglycemia

(See "Gestational diabetes mellitus: Screening, diagnosis, and prevention", section on 'Screening for overt diabetes in early pregnancy'.)

Infection — Symptomatic patients should be tested for the suspected infection. The following discussion applies to selection of asymptomatic patients for screening.

Hepatitis A — In the United States, hepatitis A vaccination during pregnancy is recommended for patients at high risk for infection [91] (see "Hepatitis A virus infection in adults: Epidemiology, clinical manifestations, and diagnosis", section on 'Epidemiology'), such as those with:

●Planned international travel

●Use of illicit drugs (injection or noninjection)

●Occupational risk for infection (eg, daycare center, residential institution, military personnel)

●Close contact with an international adoptee or persons experiencing homelessness

●Concern for a severe outcome from hepatitis A virus (HAV) infection (eg, personal history of chronic liver disease or HIV)

Prevaccination serology to determine preexisting immunity to HAV is generally not warranted but is reasonable for individuals with a high likelihood of prior HAV exposure. This is discussed in detail elsewhere. (See "Hepatitis A virus infection: Treatment and prevention", section on 'Role of prevaccine serology'.)

Measles — In areas of ongoing measles outbreaks with sustained transmission in close-knit communities, serologic testing for measles immunoglobulin G (IgG) in pregnant patients without documented immunity to measles is reasonable [92]. Any of the standard serologic assays for measles-specific IgG may be used for laboratory documentation. (See "Measles: Clinical manifestations, diagnosis, treatment, and prevention", section on 'Pregnant women' and "Measles: Clinical manifestations, diagnosis, treatment, and prevention", section on 'Diagnosis'.)

For patients not at high risk of measles exposure, evidence of immunity includes documentation of age-appropriate completion of the measles-mumps-rubella (MMR) vaccination (at least one dose of live measles-containing vaccine), laboratory evidence of immunity, or laboratory confirmation of measles [93,94]. For patients at high risk of measles exposure (eg, health care workers, students at post-high school institutions, international travelers), evidence of immunity is similar except at least two doses of a live measles-containing vaccine are required [93]. However, if laboratory evidence of immunity is available, this is sufficient documentation of immunity, regardless of the number of doses of vaccine previously administered.

Pregnant people without documented evidence of immunity should be immunized postpartum, as MMR is a live vaccine. (See "Measles, mumps, and rubella immunization in adults".)

Gonorrhea — All pregnant people aged <25 years and those aged ≥25 years at increased risk for gonorrhea should be screened for Neisseria gonorrhoeae at the first prenatal visit [51,61]. Risk factors for sexually transmitted infection are listed in the table (table 11). Clinicians should consult local public health authorities for information on groups that are more vulnerable to gonorrhea acquisition based on local disease prevalence [61].

NAAT is the preferred test for the microbiologic diagnosis of N. gonorrhoeae because of its superior accuracy; a swab is used to collect a vaginal or endocervical specimen for testing. (See "Clinical manifestations and diagnosis of Neisseria gonorrhoeae infection in adults and adolescents".)

Pregnant patients who test positive are treated immediately and retested in three months. (See "Treatment of uncomplicated gonorrhea (Neisseria gonorrhoeae infection) in adults and adolescents".)

Tuberculosis — Asymptomatic patients are screened for latent tuberculosis infection (LTBI) during pregnancy when one of the following significant risk factors for progression to active disease, which would justify prompt treatment for LTBI, is present [95]:

●Suspicion for recent TB infection based on epidemiologic exposure

●Significant immunocompromise, such as HIV infection or profound immunosuppressive therapy

Tools for diagnosis of latent TB include tuberculin skin tests (TSTs) and interferon-gamma release assays (IGRAs). An IGRA is preferred for patients with history of Bacillus Calmette-Guerin vaccination and for individuals from groups that historically have poor rates of return for skin test reading. The procedure for and interpretation of these tests and management of patients with positive test results are described separately. (See "Tuberculosis infection (latent tuberculosis) in adults: Approach to diagnosis (screening)" and "Tuberculosis disease (active tuberculosis) in pregnancy".)

Toxoplasmosis — Whether all pregnant people should undergo serological screening for toxoplasmosis is controversial. It is a routine practice is some areas with a high prevalence of infection, but this is uncommon. Maternal acquisition of toxoplasmosis is via environmental exposure (eg, ingestion of unwashed fruit or vegetables contaminated with oocytes in soil or water) and ingestion of undercooked or cured meat from infected animals. (See "Toxoplasmosis and pregnancy".)

Bacterial vaginosis — ACOG, USPSTF, CDC, and Society of Obstetricians and Gynaecologists of Canada among others suggest not routinely screening and treating all pregnant individuals with asymptomatic bacterial vaginosis to prevent preterm birth and its consequences [96-100]. Whether patients with a history of prior preterm birth should be screened for bacterial vaginosis and treated (if positive) is controversial as a reduction in recurrent preterm birth is unproven. (See "Spontaneous preterm birth: Overview of interventions for risk reduction", section on 'Routinely screening for cervicovaginal and sexually transmitted infections'.)

Trichomonas vaginalis — Although screening for Trichomonas vaginalis is not recommended as a routine component of prenatal care for asymptomatic HIV-negative individuals, those with HIV infection and those aged ≤35 years residing in a correctional facility should be screened for trichomonas at the first prenatal visit and treated if infected [61]. Trichomoniasis in individuals with HIV is associated with an increased risk of vertical and horizontal transmission of HIV. Testing should be repeated three months after treatment. (See "Trichomoniasis: Clinical manifestations and diagnosis".)

Herpes simplex virus — For pregnant people with no history of a previous herpes simplex virus (HSV) infection, serologic screening has been proposed to accurately identify two groups of individuals:

●Those who are truly HSV negative, so they can take precautions to avoid acquiring the infection

●Those who are HSV positive, so they can be offered suppressive antiviral therapy, carefully examined for lesions at the onset of labor, and offered cesarean birth, if indicated (eg, lesions are present)

Although accurate type-specific serologic tests are available to identify these individuals [101-103] and guide counseling, expert panels have recommended against universal serologic screening [61,103-105]. Available evidence indicates that screening for HSV would not meet usual criteria for an effective preventive strategy [106-108], as has been demonstrated in other infections, such as HIV and HBV [109-111]. (See "Genital herpes simplex virus infection and pregnancy", section on 'Screening pregnant women with no HSV history'.)

Cytomegalovirus — ACOG [112] and SMFM [113] recommend against routine serological screening for cytomegalovirus (CMV). Proponents of universal screening argue that knowledge of negative serology and provision of CMV counseling increase some patients' motivation to practice good hygiene and thus decrease the risk of seroconversion during pregnancy. There is also emerging evidence of possible fetal benefit from maternal pharmacotherapy. (See "Cytomegalovirus infection in pregnancy", section on 'Role of maternal screening'.)

Testing pregnant people for CMV is indicated:

●As part of the diagnostic evaluation of mononucleosis-like illnesses (see "Infectious mononucleosis", section on 'Clinical manifestations')

●If a fetal anomaly suggestive of congenital CMV infection is detected on prenatal ultrasound examination (see "Cytomegalovirus infection in pregnancy", section on 'Fetal issues')

●If the patient requests the test

Zika — In areas with no mosquito-borne Zika virus transmission, health care providers should ask all pregnant patients about possible exposure:

●Residence in or travel to an area where mosquito-borne transmission of Zika virus infection has been reported, or

●Unprotected sexual contact with a person who meets these criteria

Pregnant patients should be tested within 12 weeks of possible exposure, regardless of symptoms. Issues related to diagnostic evaluation of pregnant patients with Zika virus exposure are reviewed in detail separately. (See "Zika virus infection: Evaluation and management of pregnant patients".)

COVID-19 — SARS-CoV-2 viral testing is not routinely performed in asymptomatic patients in the community based on pregnant status alone. Indications for testing are reviewed separately. (See "COVID-19: Epidemiology, virology, and prevention", section on 'Testing and masking precautions'.)

Routine performance upon admission to labor and delivery depends on symptoms, the prevalence of COVID-19 in the community, and the patient's vaccination status. (See "COVID-19: Intrapartum and postpartum issues", section on 'Approach to infection control'.)

Chagas disease — Screening for Chagas disease is recommended for females of reproductive age who were born in or lived in a region of Mexico, South or Central America with endemic Chagas disease (table 12) [114]. Infected individuals are often unaware of their infection and the potential seriousness of the condition (eg, maternal cardiovascular/gastrointestinal complications, transmission to the fetus, hydrops fetalis). Ideally, screening is performed before pregnancy because antitrypanosomal drugs prevent congenital infection and are contraindicated during pregnancy. If prepregnancy screening was not performed, testing in pregnancy is still useful because early diagnosis and treatment of infected infants improves the prognosis of congenital Chagas disease and maternal treatment can be initiated postpartum, if appropriate. (See "Chronic Chagas cardiomyopathy: Clinical manifestations and diagnosis" and "Chagas disease: Epidemiology, screening, and prevention", section on 'Vertical transmission' and "Chagas disease: Acute and congenital Trypanosoma cruzi infection" and "Chagas disease: Chronic Trypanosoma cruzi infection".)

Lead level — Selective screening is indicated if the clinician has reason to suspect that the patient has any of the characteristics in the table (table 13), which increase the likelihood of lead exposure and increased blood lead levels [115,116].

If the blood lead level is <5 mcg/dL, no follow-up testing is needed. Otherwise, follow-up testing depends on the initial level (table 14) [115]. At birth, the pediatric provider should be informed of the mother's blood lead level (see "Childhood lead poisoning: Exposure and prevention", section on 'Prenatal exposure'). The management of elevated blood lead levels in pregnancy is discussed separately. (See "Occupational and environmental risks to reproduction in females: Specific exposures and impact", section on 'Lead' and "Lead exposure, toxicity, and poisoning in adults".)

Slight elevations of blood lead levels in pregnant people are of concern because of the potential for adverse effects on the mother and fetus (spontaneous abortion, gestational hypertension, LBW, impaired neurodevelopment). Major organizations in the United States recommend against universal lead level screening in pregnancy because the prevalence of blood lead levels over 5 mcg/dL in this setting is less than 1 percent [115,116]. The USPSTF concluded that evidence is insufficient to assess the balance of benefits and harms of screening for elevated blood lead levels in asymptomatic pregnant persons [117].

REFERRALS — Referrals in the following areas should be considered, depending on individual patient needs and the expertise and resources of the obstetric provider's practice.

●Maternal-Fetal Medicine, for high-risk pregnancies (eg, those with significant medical, surgical, or pregnancy conditions). For patients with chronic medical disorders, additional referral to a specialist in medicine or surgery may be indicated. (See 'Care provider' above.)

●Registered dietician, for nutritional and other dietary guidance (eg, issues regarding medically indicated or self-imposed diets, gestational weight gain) (See "Nutrition in pregnancy: Assessment and counseling".)

●Social Services/case management, to help with social, economic, or lifestyle issues. These include but are not limited to providing mental health assessment, counseling/support, crisis intervention, and referral; assistance accessing community services (eg, housing, transportation, utilities, childcare and parenting, food [eg, Women, Infants, & Children (WIC) Nutrition Program], health insurance [eg, Medicaid], education, treatment of substance use disorders, safety from interpersonal violence); assistance understanding insurance benefits and local maternity-related regulations (eg, Family Medical Leave Act, Occupational Safety and Health Administration protections); and assistance finding benefits that the patient may be eligible to receive.

●Genetics counselor, for patients at increased risk of a fetal disorder/abnormality because of a potential heritable disorder, exposure to a potential teratogen, or prior stillbirth. (See "Genetic counseling: Family history interpretation and risk assessment".)

●Dental services, for patients who have not attended to their oral health. (See "Oral and systemic health" and "Spontaneous preterm birth: Overview of risk factors and prognosis", section on 'Infection'.)

HEALTH EDUCATION AND HEALTH PROMOTION — Health education and promotion, including clinical practice issues, diet/nutrition/supplements, health-promoting behaviors, gestational weight gain, immunization, common patient concerns (eg, sexual activity, travel, employment, exercise, pets), management of common pregnancy-related discomforts, and medication use, are reviewed in detail separately. (See "Prenatal care: Patient education, health promotion, and safety of commonly used drugs".)

Information on preparation for childbirth is also provided separately. (See "Preparation for childbirth" and "Breastfeeding: Parental education and support".)

SPECIAL POPULATIONS

●Adolescents — (See "Pregnancy in adolescents".)

●Advanced maternal age — (See "Effects of advanced maternal age on pregnancy" and "Management of pregnancy in patients of advanced age".)

●Incarcerated pregnant people — (See "Prenatal care: Incarcerated females".)

●Patients with disabilities — The American College of Obstetricians and Gynecologists (ACOG) provides resources for obstetricians serving pregnant patients with disabilities [118]. General issues regarding care of adults with disabilities are discussed separately. (See "Primary care of the adult with intellectual and developmental disabilities" and "Disability assessment and determination in the United States".)

●Grand multiparity — (See "Grand multiparity".)

●Patients with obesity — (See "Obesity in pregnancy: Complications and maternal management".)

●Patients with acute or chronic medical or psychiatric disorders — Refer to pregnancy section of individual topic reviews on the specific disorder.

●Patients with substance use disorders — (See "Substance use during pregnancy: Overview of selected drugs" and "Opioid use disorder: Overview of treatment during pregnancy" and "Alcohol intake and pregnancy".)

●Multiple gestation — (See "Twin pregnancy: Overview" and "Twin pregnancy: Routine prenatal care" and "Triplet pregnancy".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: General prenatal care".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Prenatal care (The Basics)" and "Patient education: Activity during pregnancy (The Basics)")

●Beyond the Basics topics (see "Patient education: Avoiding infections in pregnancy (Beyond the Basics)" and "Patient education: Should I have a screening test for Down syndrome during pregnancy? (Beyond the Basics)" and "Patient education: Group B streptococcus and pregnancy (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Effectiveness – Prenatal care confers some health benefits, although how it does so and the types and magnitude of these benefits appear to be complex and multifactorial. It has many components, and the effectiveness of many of these components or packages of components generally has not been evaluated in randomized trials. (See 'Effectiveness' above.)

●Goals – The major goal of prenatal care is to help ensure the birth of a healthy newborn while minimizing maternal risk. This requires identification of individuals at increased risk of medical or obstetric complications; anticipation of problems, with intervention (if possible) to prevent or minimize morbidity; and health promotion, education, support, and shared decision-making. (See 'Goals' above.)

This is achieved, in part, by taking a comprehensive medical, obstetric, psychosocial, and family history; establishing an accurate estimated date of delivery; and appropriate laboratory testing. Forms can be helpful for this purpose. (See 'Components of the initial prenatal visit' above.)

●Timing – Prenatal care should be initiated in the first trimester, ideally by 10 weeks of gestation. (See 'Timing' above.)

●Care provider(s) – Prenatal care is generally provided to individual patients by midwives, obstetrician-gynecologists, or family medicine clinicians. Group prenatal care is an appealing alternative for some patients. Referral to a maternal-fetal medicine (MFM) specialist is appropriate for patients with chronic health conditions, patients who have experienced pregnancy complications in the past, and patients who develop complications during their current pregnancy. (See 'Care provider' above.)

●Use of ultrasound – Routine early (before 20 weeks of gestation) ultrasound examination provides better estimation of gestational age than menstrual dates (calculator 1 and calculator 2), resulting in reduced frequency of labor induction for postterm pregnancy and use of tocolysis for suspected preterm labor. Early ultrasound examination can lead to earlier detection of clinically unsuspected fetal malformations and multiple pregnancy. (See 'Calculating the estimated date of delivery' above and 'Ultrasound examination' above.)

In patients with risk factors for ectopic pregnancy (table 2), early identification of the location of the pregnancy is important. (See "Ectopic pregnancy: Epidemiology, risk factors, and anatomic sites", section on 'Risk factors' and "Ectopic pregnancy: Clinical manifestations and diagnosis", section on 'Diagnostic evaluation'.)

●History and physical examination – A thorough history and physical examination includes the past obstetric history (table 1); medication review (table 3); and screening for substance use (table 4), depression and anxiety (table 5 and figure 1A-B), and abuse or assault (table 9). Calculating body mass index (calculator 3) facilitates counseling about the appropriate amount of weight gain over the course of pregnancy (table 10). (See 'History' above and 'Physical examination' above.)

●Standard laboratory panel – The following tests are performed on all pregnant people at the initial prenatal visit (see 'Laboratory tests' above):

•RhD type and red blood cell antibody screen.

•Hematocrit/hemoglobin and mean corpuscular volume (MCV).

•Documentation of immunity to rubella and varicella.

•Qualitative assessment of urine protein.

•Assessment for asymptomatic bacteriuria. We suggest urine culture.

•Cervical cancer screening according to standard guidelines.

•Testing for syphilis (algorithm 2), hepatitis B antigen (algorithm 3), hepatitis C antibody, and chlamydia.

•Opt-out approach to HIV testing.

●Laboratory screening

•Aneuploidy screening – All pregnant people are offered aneuploidy screening or a diagnostic invasive procedure (genetic studies on samples obtained by chorionic villus biopsy or amniocentesis) before 20 weeks of gestation, regardless of maternal age.

Screening tests fall into two categories: (1) Assessment of maternal serum levels of specific biochemical markers associated with trisomy 21 (Down syndrome), with or without assessment of specific ultrasound markers and (2) Assessment of cell-free DNA in the maternal circulation. Either approach is acceptable as long as the patient receives appropriate pretest genetic counseling to make an informed choice and is aware that costs may differ substantially. (See 'Aneuploidy screening and diagnosis' above.)

•Carrier screening

-Ethnic versus panethnic – An ethnic-specific or panethnic approach may be taken for carrier screening; however, an ethnic-based approach is not considered reliable in some countries because of the increasingly diverse ethnic distribution of the population.

-Cystic fibrosis and spinal muscular atrophy – All patients are offered genetic carrier screening for cystic fibrosis and spinal muscular atrophy, either alone or as part of an expanded carrier screening panel. (See 'Carrier screening' above.)

-Hemoglobinopathy – Red cell indices are used to screen for carriers of hemoglobinopathies; an MCV less than 80 femtoliters (fL) in the absence of iron deficiency denotes patients at increased risk for alpha or beta thalassemia. However, a complete blood count (CBC) and MCV may not detect carriers of hemoglobin S, C, or E; thus, maternal hemoglobin analysis by either high-performance liquid chromatography (HPLC) or isoelectric focusing (IEF) is recommended to identify these abnormal hemoglobins.

•Thyroid disease and diabetes – Patients at increased risk of thyroid disorders (hypo- or hyperthyroidism) or type 2 diabetes mellitus are screened for these disorders. (See 'Thyroid function' above and 'Type 2 diabetes' above.)

•Infection – Patients at increased risk of specific infectious diseases are screened for these disorders. Risk factors for a sexually transmitted infection are listed in the table (table 11). (See 'Infection' above.)

•Lead – Lead level screening is indicated in patients at risk for lead exposure (table 13). If the blood lead level is <5 mcg/dL, no follow-up testing is needed. Otherwise, follow-up testing depends on the initial level (table 14). (See 'Lead level' above.)