Version July 2025
INTRODUCTION —
Postterm infants are born at a gestational age (GA) greater than 42 weeks or ≥294 days from the first day of the last menstrual period. Postterm infants have higher rates of morbidity and mortality than term infants.
The epidemiology, clinical manifestations, neonatal management, and outcome of postterm infants will be reviewed here. In this review, we use the terms "mother" and "maternal" to refer to the birthing parent, in agreement with the common style used in the medical literature. However, clinicians should be sensitive to individual language preferences in discussions with parents/caregivers.
Maternal and fetal issues related to postterm pregnancy and management of postterm pregnancies are reviewed separately. (See "Postterm pregnancy".)
INCIDENCE —
The incidence of postterm births varies with different patient populations and is dependent on a number of factors, such as the percentage of primigravid individuals, and local practice patterns regarding the rates of scheduled cesarean delivery and routine labor induction. (See "Postterm pregnancy", section on 'Prevalence'.)
●In the United States, postterm births have decreased from 11 percent of all births in 1990 to 5.5 percent of births in 2009 [1]. The overall incidence has decreased with the increased use of first trimester ultrasounds and the resultant improved dating of pregnancies [2].
●In a population-based Norwegian study, the reported incidence of postterm deliveries was 7.6 percent from 1989 to 1999 [3].
●In a study from a tertiary medical center in Israel, 3.2 percent of uncomplicated singleton births were born postterm (gestational age [GA] ≥42 weeks), 19.7 percent were born late term (GA between 41 and <42 weeks), and 77.1 were full-term (GA between 39 and <41 weeks) [4].
●While there is no difference in incidence between males and females when dating is performed by last menstrual period, one large study concluded that when midtrimester ultrasound dating is employed, more females are born postterm [5], perhaps due to an underestimation of gestational age for female fetuses based on their smaller size [5].
In the United States, the decline in postterm births is the result of the widespread practice of inducing labor once pregnancies reach 41 weeks, a specific effort to avoid the delivery of postterm infants. (See "Postterm pregnancy", section on 'Management'.)
RISK FACTORS —
The etiology of most postterm pregnancies is unknown. Risk factors for postterm births are discussed separately and include the following (see "Postterm pregnancy", section on 'Etiology'):
●Primigravidity.
●Prior postterm pregnancy.
●Genetic predisposition as concordance for postterm pregnancy is higher in monozygotic than dizygotic twin mothers.
●Maternal obesity.
●Older maternal age.
●Male fetal sex.
●Specific conditions in the offspring associated with prolonged gestation include adrenal gland hypoplasia and congenital adrenal hyperplasia due to 21-hydroxylase deficiency [6]. Placental sulfatase deficiency also is a rare cause of postterm pregnancy.
It has been suggested that specific nutritional deficiencies, such as zinc, may predispose to altered pregnancy length, but systematic reviews of the available literature have not supported this finding [7]. It has also been suggested that a specific genetic factor may be associated with postterm birth, although none has yet been identified [8-10].
CLINICAL MANIFESTATIONS —
The clinical presentation of postterm infants is based primarily on fetal growth. In most cases, continued fetal growth results in higher birth weights in the postterm than term infant, with an increased likelihood of macrosomia. However, fetal growth restriction (FGR) occurs in some postterm infants, most likely caused by a poorly functioning placenta that is unable to provide adequate nutrition [11-13]. This results in the birth of a small for gestational age (SGA) infant, who usually appears malnourished. (See 'Fetal growth restriction' below.)
Macrosomia — Infant size and birth weight (BW) are affected by extended gestational length. Most postterm infants are larger than term infants [14-16], as both fetal BW and head circumference measurements continue to increase from 39 to 43 weeks gestation [17]. In a study from China, macrosomia (defined as a BW >4000 g) was more likely in postterm infants (gestational age [GA] ≥42 weeks) than in infants born at 40 weeks gestation (11 versus 9 percent, adjusted odds ratio [OR] 1.35, 95% CI 1.3-1.41) [16].
These infants appear normal at birth, apart from their large size. They often have accentuated physiologic desquamation of the skin, which peaks at approximately one week of age. Postterm macrosomic infants are at risk for birth injury due to prolonged labor, cephalopelvic disproportion, and shoulder dystocia [15]. (See "Large for gestational age (LGA) newborn", section on 'Birth injury' and 'Neonatal morbidity' below.)
Fetal growth restriction — Poor fetal growth is thought to be due to a degenerating or poorly functioning placenta that is unable to provide adequate nutrition and oxygenation. The risk of FGR increases as the pregnancy extends beyond 40 weeks gestation. As an example, in a population-based study of all deliveries that occurred in Sweden from 1987 to 1992, the incidence of FGR was 17, 20, 29, and 62 per 1000 pregnancies at gestational weeks 40, 41, 42, and ≥43, respectively [18]. Fetal growth restriction is associated with increased perinatal mortality in postterm pregnancies. (See 'Perinatal mortality' below.)
FGR in postterm pregnancy results in a long, thin, SGA, malnourished infant with meconium staining, and dry and parchment-like peeling skin, referred to as dysmaturity syndrome [11,19,20]. In these infants, the skin appears loose, especially over the thighs and buttocks, and has prominent creases. Vernix caseosa is decreased or absent. Lanugo hair is sparse or absent, while scalp hair is increased. The nails typically are long. The infants generally have the appearance of increased alertness and a "wide-eyed" look. (See "Fetal growth restriction (FGR) and small for gestational age (SGA) newborns", section on 'Clinical findings'.)
COMPLICATIONS
Perinatal mortality — Perinatal mortality (ie, stillbirths plus early neonatal deaths) increases as the pregnancy extends beyond 40 weeks gestation [3,18,21-23] (see "Postterm pregnancy", section on 'Perinatal mortality'):
●In a population-based study from Norway, perinatal mortality was twofold greater in infants born at ≥42 weeks gestation compared with term infants (relative risk [RR] 2.0, 95% CI 0.9-4.6) [3]. In the previously discussed population-based study from Sweden, intrauterine fetal death (stillbirth) rate rose with increasing gestational age (GA) beyond 40 weeks [18]. Although not statistically significant, there was a trend of increased neonatal mortality with increasing GA above 40 weeks. The presence of fetal growth restriction (FGR) increased the risk of both fetal and neonatal mortality as GA increased beyond 40 weeks. The analysis adjusted for maternal age, parity, maternal smoking, and fetal sex. A large population-based cohort study confirmed the significance of growth restriction as the major mortality risk in these infants [22].
●In a large retrospective study of singleton liveborn infants without congenital anomalies in California from 1999 to 2003, infants born between 41 and <43 weeks gestation had a higher mortality rate than those born between 38 and 40 weeks gestation (adjusted odds ratio [OR] 1.34, 95% CI 1.08-1.65) [23]. The neonatal death rates were 2.46, 2.7, 2.54, 3.66, and 3.28 per 10,000 live births for infants born between 38 and <39 weeks, 39 and <40 weeks, 40 and <41 weeks, 41 and <42 weeks, and 42 and <43 weeks, respectively.
Fetoplacental insufficiency resulting in poor fetal growth, asphyxia (with and without meconium), and intrauterine infection are thought to contribute to increased perinatal mortality [18,24].
Other factors concomitant with prolonged pregnancy that have been reported to be associated with increased perinatal mortality include:
●Primigravidity – In one study, stillbirth risk did not differ by parity prior to 41 weeks gestation. However, the stillbirth risk was greater in nulliparous as compared with multiparous women at >42 weeks gestation (RR 2.9, 95% CI 1.06-8.19) [25].
●Older maternal age – In a population-based study from Norway, the risk of postterm fetal death was greater in mothers aged 40 years compared with younger mothers <20 to 34 years of age, and 35 to 39 years of age (1.2 versus 0.3 and 0.5 percent) [26].
Neonatal morbidity — The risk of neonatal complications is greater in postterm compared with term infants. Among postterm infants, the types of complications tend to depend on how fetal growth has been affected.
●Fetal macrosomia – Fetal macrosomia is associated with prolonged labor, cephalopelvic disproportion, perinatal asphyxia, neonatal encephalopathy, and shoulder dystocia resulting in an increased risk of orthopedic (eg, clavicular fractures) or neurologic birth injury (eg, brachial plexus palsy). (See "Large for gestational age (LGA) newborn", section on 'Complications'.)
●Fetal growth restriction – Postterm infants who had fetal (intrauterine) growth restriction (FGR) are at increased risk of perinatal asphyxia and neonatal encephalopathy, as the associated oligohydramnios may predispose to umbilical cord compression. Affected infants are at risk for neonatal complications typically seen in small for gestational age infants (SGA), such as hypoglycemia and polycythemia. (See "Fetal growth restriction (FGR) and small for gestational age (SGA) newborns", section on 'Neonatal complications'.)
Postterm infants are more likely than term infants to have low Apgar scores, an indirect measure of perinatal asphyxia [3,27,28]. Meconium aspiration, congenital malformations, and persistent pulmonary hypertension are also more frequently observed in postterm infants [27,29]. (See "Meconium aspiration syndrome: Pathophysiology, clinical manifestations, and diagnosis" and "Persistent pulmonary hypertension of the newborn (PPHN): Clinical features and diagnosis".)
●In one autopsy study, postterm infants were more likely than control term infants to have evidence of aspiration of amniotic fluid and/or meconium, which may have contributed to respiratory failure and death [30].
●A large study that examined over 665,000 singleton births found an increased risk of oligohydramnios, meconium stained fluid, and birth trauma including facial nerve palsy in infants born postterm compared with term counterparts [31].
Other complications have also been reported. In the previously mentioned retrospective study from a tertiary Israeli hospital of 23,524 singleton births, multivariable analysis showed postterm birth (gestational age [GA] ≥42 weeks) was independently associated with an increased risk of neonatal intensive care admission, respiratory morbidity, culture-positive sepsis, and administration of antibiotic treatment compared with both infants born full-term (GA between 39 and <41 weeks) and late-term (GA between 41 and <42 weeks) [4]. Postterm infants also were more likely to have hypoglycemia compared with full-term but not late-term infants.
NEONATAL MANAGEMENT —
Because the optimal intervention is prevention of postterm births, it has been suggested that induction of labor be routinely performed in mothers who are at 41 weeks gestation. (See "Postterm pregnancy", section on 'Our approach: Induction at 41+0 weeks'.)
Nevertheless, there are settings in which induction of labor at 41 weeks gestation is not an option. For these postterm deliveries, neonatal management consists of screening and treating complications associated with prolonged pregnancy (eg, meconium aspiration, perinatal asphyxia, and persistent pulmonary hypertension), and providing routine newborn care.
●Assessment prior to delivery – Prior to delivery, an assessment of the need for neonatal resuscitation is made based on the gestational age (GA), anticipated birth weight (BW), presence of a congenital anomaly or labor complications, mode of delivery (eg, cesarean delivery), and maternal history. (See "Neonatal resuscitation in the delivery room", section on 'Anticipation of resuscitation need'.)
●Initial evaluation after delivery – Immediately after delivery, routine neonatal care is provided that includes drying, clearing the airway of secretions if present, maintaining warmth, and a rapid assessment of the infant's clinical status based on vigor, including cry, heart rate, and tone, as well as a physical examination to identify any major congenital anomaly.
The need for further intervention is based on this initial evaluation. If the infant does not require additional resuscitation, the infant should be returned to the mother for skin-to-skin care and initiation of breastfeeding right after birth. Infants should be fed as quickly as possible after delivery to avoid hypoglycemia. (See "Neonatal resuscitation in the delivery room", section on 'Resuscitation' and "Overview of the routine management of the healthy newborn infant", section on 'Delivery room care'.)
●Assessment following delivery – Further evaluation following transition from the delivery room includes a comprehensive examination to identify any evidence of birth trauma (eg, perinatal depression, brachial plexus injury, or clavicular fracture), congenital defects, or complications associated with prolonged pregnancy. (See 'Neonatal morbidity' above and "Neonatal birth injuries" and "Perinatal asphyxia in term and late preterm infants".)
●Screening tests – Laboratory screening for hypoglycemia and polycythemia should be performed in infants with evidence of poor fetal growth within the first one to two hours following delivery. (See "Pathogenesis, screening, and diagnosis of neonatal hypoglycemia", section on 'Screening' and "Neonatal polycythemia", section on 'Diagnosis' and 'Neonatal morbidity' above.)
●Routine newborn care – If there are no significant complications that require further intervention, routine newborn care should be provided. (See "Overview of the routine management of the healthy newborn infant".)
LONG-TERM OUTCOME —
Evidence on the long-term outcome of postterm infants is limited. Based on the available data, the long-term effects on the offspring of prolonged pregnancies remain uncertain.
Some data suggest that these patients may be at risk for neurodevelopmental complications:
●Cerebral palsy (CP) – Children born postterm appear to have an increased risk of CP compared with those who were born at term. This was illustrated in a population-based follow-up study from Norway that reported children born at a gestational age (GA) >42 weeks were more likely to develop CP than children born at 40 weeks gestation (relative risk [RR] 1.4, 95% CI 1.1-1.8) [32]. The prevalence of CP in children with a GA >42 weeks was 1.44 per 1000 patients. (See "Cerebral palsy: Epidemiology, etiology, and prevention".)
●Epilepsy – In a cohort Danish study, it appears that prolonged gestation was a risk factor for early epilepsy that occurred within the first year of life [33]. However, there was no evidence of an association between postterm birth and epilepsy beyond one year of age. A large Swedish study examining over 1 million births between 1983 and 1993 identified a higher incidence of childhood epilepsy (diagnosed up to age 20) among infants born postterm [34].
●Developmental outcome – In an older cohort study from 1977, postterm infants had comparable motor scores on the Bayley Scales of Infant Development at eight months of age compared with controls, but cognitive scores were lower [35]. Such older studies may underestimate the impact of postterm birth, because they were done before routine ultrasound dating was in use. Many pregnancies may have been misclassified as postterm, resulting in an artifactual reduction in the estimated complication rates among postterm infants. In a subsequent meta-analysis including 13 studies published between 1969 and 2017, postterm birth was associated with a small but statistically significant adverse effect on cognitive outcomes [36]. However, there was limited evidence to suggest an adverse effect on developmental or educational outcomes.
●Behavioral problems – In a cohort study of infants in the Netherlands, the risk of behavioral problems and attention deficit hyperactivity disorder was increased among postterm infants, compared with term counterparts [37].
In contrast, other studies report comparable neurodevelopmental outcomes for postterm and term infants:
●At one and two years of age, the general intelligence quotient, physical milestones, and frequency of intercurrent illnesses were similar in postterm and term infants [13]. In a large retrospective study, the risk of general neurologic disability was similar in term and postterm infants, although there was some increased risk of intellectual disability among the postterm infants [38].
●In an older case-controlled study from 1977, Black children who were diagnosed with dysmaturity syndrome at birth had similar mental and physical development at seven years of age compared with controls [39].
In a study comparing linked data from Florida birth certificates and public school records of children born at 41 weeks (late term) with those of children born at 39 or 40 weeks, children born late term were more likely to have higher average test scores in mathematics and reading at ages 8 through 15 years of age [40]. However, they were more likely to be physically impaired. Although these data are not directly applicable to children born postterm, they provide indirect evidence of poorer physical outcomes as pregnancy extends beyond term gestation (39 to 40 weeks).
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 5th to 6th 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 10th to 12th 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: When your baby is overdue (The Basics)")
●Beyond the Basics topics (see "Patient education: Postterm pregnancy (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS —
Postterm infants are born at a gestational age (GA) greater than 42 weeks or 294 days from the first day of the last menstrual period.
●Risk factors for postterm delivery – Risk factors for postterm delivery include maternal factors (eg, primigravidity, prior delivery of a postterm infant, maternal obesity, and older maternal age), neonatal factors (eg, male sex and adrenal gland defects), and placental factors (eg, sulfatase deficiency). (See 'Risk factors' above.)
●Clinical features of postterm infants – The clinical presentation of postterm infants is dependent on fetal growth.
•In most cases, continued fetal growth leads to larger size infants for postterm compared with term deliveries and is associated with an increased risk of macrosomia (ie, birth weight [BW] >4500 g). (See 'Macrosomia' above.)
•Fetal growth restriction (FGR) occurs in some postterm infants, resulting in the birth of a small for gestational age (SGA), malnourished infant with meconium staining and dry, peeling skin (referred to as dysmaturity syndrome). (See 'Fetal growth restriction' above.)
●Perinatal mortality – Perinatal mortality rises as pregnancy extends beyond 40 weeks gestation. The presence of FGR increases the risk of perinatal mortality. (See 'Perinatal mortality' above.)
●Neonatal morbidity – The risk of neonatal complications is greater in postterm compared with term infants. Macrosomic postterm infants are at risk for birth injuries that are primarily due to shoulder dystocia and include brachial plexus injury and clavicular fractures. In postterm infants with FGR, complications include hypoglycemia and polycythemia. All postterm infants are at risk for perinatal asphyxia, meconium aspiration, and persistent pulmonary hypertension. (See 'Neonatal morbidity' above.)
●Neonatal care – Neonatal management of postterm infants includes screening and treating complications associated with prolonged pregnancy and providing routine newborn care. (See 'Neonatal management' above.)
●Long-term outcomes – The long-term effects of prolonged pregnancies remain uncertain. Limited data suggest individuals born postterm are at risk for neurodevelopmental complications (eg, cerebral palsy [CP]). (See 'Long-term outcome' above.)
ACKNOWLEDGMENT —
The UpToDate editorial staff acknowledges Lori A Sielski, MD, who contributed to an earlier version of this topic review.
