Polyhydramnios: Etiology, diagnosis, and management in singleton gestations

INTRODUCTION — Polyhydramnios (also known as hydramnios) refers to an excessive volume of amniotic fluid. It should be suspected clinically when uterine size is large for gestational age (fundal height [cm] that exceeds the weeks of gestation by >3). Prenatal diagnosis is based upon noninvasive sonographic documentation of excessive amniotic fluid volume (AFV) by a quantitative technique, such as amniotic fluid index (AFI) ≥24 cm or single deepest pocket (SDP) ≥8 cm.

Polyhydramnios can be idiopathic or related to a variety of maternal and fetal disorders [1-3]. Potential consequences include increased risks for preterm birth, fetal malposition, placental abruption and/or cord prolapse.

This topic will discuss issues related to polyhydramnios in singleton gestations. Methods of AFV assessment are reviewed separately. (See "Assessment of amniotic fluid volume".)

INCIDENCE — The incidence of polyhydramnios in a general obstetric population generally ranges from 1 to 2 percent [4-9]. Reported rates are highly influenced by the gestational age at the time of the ultrasound examination (higher preterm, lower postterm), the population studied (low or high risk, screening or indicated ultrasound examination, antepartum or intrapartum), and variations in diagnostic criteria (use of amniotic fluid index [AFI] versus single deepest pocket [SDP]).

In a series of over 93,000 singleton pregnancies delivering over six years at a single hospital, polyhydramnios was diagnosed during antepartum sonography in 0.7 percent and was described as mild, moderate, or severe in 66, 22, and 12 percent of cases, respectively [5].

PATHOGENESIS — The volume of amniotic fluid reflects the balance between fluid production and movement of fluid out of the amniotic sac. The most common mechanisms for polyhydramnios are decreased fetal swallowing and increased urination [10-12].

Homeostatic mechanisms, such as intramembranous absorption (transfer of amniotic fluid across the amnion into the fetal circulation), work to maintain amniotic fluid volume (AFV); these mechanisms appear to be more successful in preventing polyhydramnios than in preventing oligohydramnios. (See "Physiology of amniotic fluid volume regulation".)

CONDITIONS ASSOCIATED WITH POLYHYDRAMNIOS — Polyhydramnios may be idiopathic or associated with a variety of disorders (table 1).

Fetal anomalies (often associated with an underlying genetic abnormality or syndrome) are the most common conditions associated with severe polyhydramnios, while maternal diabetes, multiple gestation, and idiopathic factors are more often associated with milder cases.

Sometimes, multiple pathways are involved in production of excess amniotic fluid. For example, congenital mesoblastic nephroma is associated with polyhydramnios in approximately 70 percent of cases and contributes to the high rate (25 percent) of preterm birth. The increased amniotic fluid may be attributed to increased urine production due to renal hyperperfusion, decreased gastrointestinal absorption due to bowel compression, or tumor secretion of prostaglandins leading to hypercalcemia-induced polyuria [13]. Rarely, cardiac failure and hydrops occur [14].

Idiopathic cases — Approximately 40 percent of polyhydramnios is idiopathic [15]. After birth, however, an abnormality is diagnosed in up to 25 percent of cases considered idiopathic prenatally [15-18]. Fetal anemia, Bartter syndrome, infection, and neuromuscular disorders account for some cases considered idiopathic prenatally, and should be considered in the differential diagnosis if a structural abnormality and maternal diabetes are excluded, although Bartter syndrome and neuromuscular diseases are quite rare, and infection (TORCH [toxoplasmosis, other, rubella, cytomegalovirus, and herpes simplex virus], parvovirus) is rarely associated with isolated polyhydramnios. In a retrospective observational study of 294 singleton pregnancies with polyhydramnios and serum screening for TORCH and parvovirus B19 infections, only two patients tested positive for parvovirus infection and only one for toxoplasmosis infection [19].

Recurrence — In a study of over 2.7 million singleton births in the Medical Birth Registry of Norway (1967 to 2017), individuals with idiopathic polyhydramnios in their first pregnancy had a 6.6-fold increase in odds of idiopathic polyhydramnios in their second pregnancy compared with those without idiopathic polyhydramnios in their first pregnancy [20]. The odds increased 12.6-fold in the third pregnancy after two previously affected pregnancies but were less if only one of the first two pregnancies had idiopathic polyhydramnios.

Fetal anomalies — Fetal anomalies account for approximately one-third of singleton pregnancies with polyhydramnios [15]. The most common anomalies interfere with fetal swallowing and/or absorption of fluid [21,22]. Obstruction of the gastrointestinal tract may be primary (eg, duodenal, esophageal, or upper intestinal atresia) or secondary (eg, massive unilateral dysplastic kidneys, large thoracic mass, diaphragmatic hernia).

Anomalies in most other organ systems have been associated with polyhydramnios, but are less common and can involve other mechanisms.

Maternal diabetes mellitus — Maternal diabetes accounts for 8 to 25 percent of pregnancies with polyhydramnios [23]. The rates of polyhydramnios in patients with versus without diabetes were 10.5 and 3.8 percent, respectively, when diagnosed by amniotic fluid index (AFI) in a large retrospective study [24]. The rate varied, in part, by type of diabetes: gestational A1 (5.4 percent), gestational A2 (13.4 percent), type 1 (21.2 percent), and type 2 (15.3 percent). All of these rates were higher when diagnosed by single deepest pocket (SDP).

The mechanism for polyhydramnios in pregnancies complicated by maternal diabetes is unclear, though it is believed that fetal hyperglycemia-induced polyuria (osmotic diuresis) is the most likely etiology. This conclusion is supported by the observation that polyhydramnios is often associated with high maternal glycated hemoglobin (A1C) levels and fetal macrosomia [25,26]. Thus, the increasing incidence of polyhydramnios from progression of diabetes A1, to A2, to type 2, to type 1 is consistent with increasing maternal (and thus fetal) serum glucose levels. Decreased fetal swallowing or an imbalance in water movement between the maternal and fetal compartments in diabetic pregnancies are other possible mechanisms.

A retrospective study including 1545 patients with polyhydramnios found that only 8.5 percent of cases could be attributed to diabetes, and those patients usually had mild polyhydramnios (defined as an AFI 26.0 to 35.9 cm) [23]. Other researchers have demonstrated that pregnancies with normal glucose tolerance tests that develop polyhydramnios and accelerated fetal growth are at higher risk for maternal and neonatal complications, while isolated polyhydramnios without accelerated growth increases the risk for birth complications but not neonatal morbidity [27].

Fetal growth restriction — When combined with polyhydramnios, fetal growth restriction (FGR) is associated with high morbidity and mortality. In a study of 153 pregnancies with FGR and polyhydramnios, four potential etiological groups were identified: chromosomal anomalies (41.8 percent, n = 64), complex malformation syndromes (24.1 percent, n = 37), isolated malformations (15.7 percent, n = 24), musculoskeletal disorders (9.2 percent, n = 14); another 9.2 percent (n = 14) had no abnormalities detected prenatally [28].

Twin-twin transfusion syndrome — Multiple gestation accounts for up to 10 percent of polyhydramnios. In monochorionic multiple gestation, polyhydramnios/oligohydramnios sequence is most suggestive of TTTS. (See "Twin-twin transfusion syndrome: Screening, prevalence, pathophysiology, and diagnosis".)

Aneuploidy — Aneuploidy is an uncommon cause of polyhydramnios [19]. The combination of fetal growth restriction and polyhydramnios is suggestive of trisomy 18; other sonographic markers of trisomy 18 are typically present. Excess amniotic fluid in this syndrome may be related to difficulty swallowing or to intestinal abnormalities. (See "Sonographic findings associated with fetal aneuploidy", section on 'Trisomy 18 (Edward syndrome)'.)

Other aneuploidies have also been associated with polyhydramnios, most commonly trisomy 21, likely related to cases with duodenal atresia. (See "Sonographic findings associated with fetal aneuploidy", section on 'Trisomy 21 (Down syndrome)'.)

In a retrospective cohort of 623 singleton pregnancies with isolated polyhydramnios, 3.1 percent (19 out of 623) were associated with clinically significant chromosomal microarray (CMA) aberrations compared with 1.4 percent of control cases (78 out of 5541) with normal ultrasound [29]. However, the risk for abnormal CMA results in the 158 cases with mild polyhydramnios (AFI 25 to 29.9, or maximal vertical pocket 8 to 11.9 cm) was similar to that from pregnancies with normal ultrasound. Among 119 cases with nonisolated polyhydramnios, abnormal CMA findings were noted in 6.7 percent of cases and were primarily karyotype-detectable. The most frequent associated anomalies involved the cardiovascular system (26.1 percent) and brain (15.1 percent).

High cardiac output states — High fetal cardiac output states can lead to increased fetal urine production, but are uncommon [19]. Fetal anemia is a common cause of a high-output state and may be due to alloimmunization, parvovirus B19 infection, a large or chronic fetomaternal hemorrhage, alpha-thalassemia, hemolysis secondary to glucose-6-phosphate dehydrogenase deficiency, and other disorders [30].

High-output states can also be caused by arteriovenous shunting (eg, sacrococcygeal teratoma, TTTS, chorioangioma) and tachyarrhythmias.

Neuromuscular disorders — Fetal neuromuscular disorders, such as anencephaly and myotonic dystrophy, are rare and generally cause polyhydramnios by interfering with swallowing [31-35]. In a retrospective study of the prenatal sonographic manifestation of congenital hypotonia, polyhydramnios was the most prominent sonographic sign, observed in 16 of 25 cases (64 percent) beginning in the late second trimester, while absent fetal tone on the last biophysical scan was observed in only two of 25 cases (8 percent) [36]. (See "Myotonic dystrophy: Etiology, clinical features, and diagnosis" and "Anencephaly" and "Approach to the infant with hypotonia and weakness" and "Overview of peripheral nerve and muscle disorders causing hypotonia in the newborn".)

Bartter syndrome — The most common antenatal type of Bartter syndrome is a rare autosomal recessive tubular disorder associated with intrauterine presentation of renal tubular hypokalemic alkalosis. As a result, the fetus develops polyuria and subsequent polyhydramnios between 24 and 30 weeks of gestation. Infants exhibit postnatal polyuria and persistent renal salt wasting, requiring lifelong treatment.

A severe but transient form of antenatal Bartter syndrome has been attributed to mutations in MAGED2, which maps to the X chromosome and appears to be essential for fetal renal salt reabsorption and maintenance of normal amniotic fluid homeostasis [37]. This X-linked disorder has very early onset of severe polyhydramnios (median 19 to 20 weeks of gestation), often resulting in preterm birth (median gestational age 22 to 34 weeks), but signs and symptoms of renal dysfunction resolve spontaneously postnatally. (See "Inherited hypokalemic salt-losing tubulopathies: Pathophysiology and overview of clinical manifestations".)

Overgrowth syndromes — In cases of excessive growth for gestational age associated with polyhydramnios, omphalocele, placentomegaly, or macroglossia, Beckwith-Wiedemann syndrome or one of the other overgrowth syndromes should be considered [38]. (See "Beckwith-Wiedemann syndrome".)

CLINICAL FINDINGS — Polyhydramnios presents with a uterine size that is large for gestational age (fundal height [cm] that exceeds the weeks of gestation by >3) or as an incidental finding on a prenatal ultrasound examination.

The increase in amniotic fluid volume (AFV) is usually asymptomatic; however, persistent shortness of breath, uterine irritability and contractions, and abdominal discomfort can occur with severe uterine distention. Symptoms may be related to mechanical factors from a very large uterus and to high amniotic fluid pressure [39,40].

DIAGNOSIS — The diagnosis of polyhydramnios is based upon sonographic visualization of increased amniotic fluid volume (AFV). We agree with recommendations from a consensus panel at a fetal imaging workshop [41] and endorsed by the Society for Maternal-Fetal Medicine [42] that suggested using either of the following thresholds for diagnosing polyhydramnios:

●Single deepest pocket (SDP) ≥8 cm or

●Amniotic fluid index (AFI) ≥24 cm

SDP and AFI can also be used to classify polyhydramnios as mild, moderate, or severe (table 2).

Although a qualitative assessment of mild, moderate, or severe polyhydramnios can be made initially, we use a quantitative approach because it provides a measurement that can be compared over serial examinations. Both SDP and AFI are the accepted standards for diagnosis and clinical management. Although these tests perform relatively poorly against quantitative measurements using dye dilution (research studies), they have been associated with an increased risk of adverse outcome and thus have clinical utility.

It appears that the SDP overdiagnoses polyhydramnios as compared with the AFI. Of note, however, AFI may overdiagnose oligohydramnios when compared with SDP [43].

POSTDIAGNOSTIC EVALUATION — The following evaluation is most appropriate for nonhydropic singletons and dichorionic twins. In monochorionic twins with polyhydramnios/oligohydramnios sequence, twin-twin transfusion syndrome is the most likely diagnosis and is reviewed separately. (See "Twin-twin transfusion syndrome: Screening, prevalence, pathophysiology, and diagnosis" and "Twin-twin transfusion syndrome: Management and outcome".)

Approach to determining the etiology of polyhydramnios:

●Obtain a detailed medical history to evaluate for heritable diseases associated with polyhydramnios. For example, arthrogryposis often presents in the second trimester with polyhydramnios and multiple congenital contractures, which should be identified by ultrasound. More than 150 genetic syndromes are associated with arthrogryposis; most cases are recessive inheritance or new pathogenic variants. If suspected, the patient should be referred to a genetics specialist for three-generation pedigree and parental examination.

In patients in whom the personal/family history suggests a hereditary anemia (eg, alpha-thalassemia) or inborn error of metabolism, testing for the relevant disorder is indicated. (See "Hemoglobinopathy: Screening and counseling in the reproductive setting and fetal diagnosis" and "Diagnosis and management of glucose-6-phosphate dehydrogenase (G6PD) deficiency", section on 'Pregnancy' and "Inborn errors of metabolism: Identifying the specific disorder".)

●Evaluate for fetal hydrops – If polyhydramnios is accompanied by hydrops, evaluation for a nonimmune or immune etiology is the priority. Fetal anemia is a common cause of hydrops and has both immune and nonimmune etiologies. (See "Nonimmune hydrops fetalis", section on 'Postdiagnostic evaluation' and "RhD alloimmunization in pregnancy: Overview", section on 'Fetal/neonatal consequences of alloimmunization'.)

●Evaluate for fetal anomalies – A detailed sonographic evaluation should be performed to look for fetal anomalies. The likelihood of identifying the etiology of polyhydramnios prenatally correlates with the severity of fluid accumulation. In one series, an etiology was determined in only 17 percent of pregnancies with mild polyhydramnios but in 91 percent of those with moderate or severe amniotic fluid accumulation [4]. In another series, the frequency of an anomalous infant in the setting of mild, moderate, and severe polyhydramnios was 8, 12, and 31 percent, respectively [5]. Overall, 80 percent of anomalous infants were detected prenatally. Anomalies most often missed included esophageal atresia with a tracheoesophageal fistula, cardiac septal defects, and cleft palate.

In cases of polyhydramnios with suspicion of esophageal atresia (small or nonvisualizable fetal stomach bubble), elevated levels of amniotic fluid gamma-glutamyl transpeptidase and alpha-fetoprotein are suggestive of the diagnosis and can be performed at the time of amniocentesis for genetic studies [44].

●Measure middle cerebral artery (MCA) post systolic velocity (PSV) – We measure the MCA-PSV in the initial evaluation of all cases of idiopathic polyhydramnios before 35 weeks of gestation, even in the absence of hydrops. Although fetal hydrops precedes polyhydramnios in the vast majority of polyhydramnios cases associated with fetal anemia, we have encountered cases of fetal anemia in which polyhydramnios preceded the appearance of hydrops.

MCA-PSV performs well from 25 to 35 weeks of gestation. Doppler findings suggestive of moderate and severe fetal anemia (MCA-PSV ≥1.5 multiples of the median [MoM]) had a false-positive rate of 12 percent in a study of 111 fetuses up to 36 weeks of gestation at risk for anemia and in whom 17 percent had severe anemia without hydrops (amniotic fluid volume [AFV] was not described) [45]. The false-positive rate is higher after 35 weeks [46] and lower if a threshold of ≥1.29 MoMs is used [47].

If MCA-PSV is ≥1.5 multiples of the median, work-up for immune and nonimmune causes of fetal anemia should be performed. (See "Nonimmune hydrops fetalis", section on 'Postdiagnostic evaluation'.)

●Offer genetic counseling and fetal genetic studies – We suggest genetic counseling and offering amniocentesis for fetal microarray in pregnancies with a congenital anomaly or severe polyhydramnios (all cases, even if apparently isolated), especially if the results will affect pregnancy management. Whether genetic studies should be offered in the absence of fetal anomalies or severe polyhydramnios is controversial as the likelihood of chromosomal abnormality is low in this setting [5].

When a fetal anomaly is present, patients are offered microarray because of the increased risk of chromosomal abnormalities in this setting. In cases of polyhydramnios associated with anomalies not known to be associated with an increased risk of chromosomal abnormalities (eg, jejunal atresia), referral to a maternal-fetal medicine specialist and/or genetic counselor can help with shared decision-making regarding microarray or other genetic examinations. (See "Prenatal genetic evaluation of the fetus with anomalies or soft markers".)

When severe polyhydramnios is present, we offer microarray because of data showing increased frequencies of congenital anomalies [5,48] and genetic abnormalities with increasing degrees of polyhydramnios. In a series of 249 singleton pregnancies with mild, moderate, or severe isolated polyhydramnios referred for amniocentesis, clinically significant microarray aberrations were detected in 5 of 91 patients with moderate or severe polyhydramnios (5.5 percent), a higher rate than that in patients with mild polyhydramnios (4 out of 158, 2.5 percent) or in a control population (1.4 percent); the rates in the latter two groups were not significantly different [29].

•Role of gene sequencing – In cases of severe polyhydramnios with a fetal anomaly and a normal microarray, gene sequencing may detect a genetic abnormality of clinical significance [49,50]. For example, Noonan syndrome is often associated with polyhydramnios, as well as other abnormalities, and can be diagnosed by gene sequencing. (See "Noonan syndrome", section on 'Genetic testing' and "Noonan syndrome", section on 'Prenatal testing'.)

●Consider Bartter syndrome – In pregnancies with a male fetus and unexplained severe polyhydramnios in the second trimester, especially with previous history of severe polyhydramnios, genetic studies for identification of pathogenic variants in MAGED2, which causes antenatal Bartter syndrome, should be offered [37]. Accurate prenatal diagnosis can avoid potentially harmful treatment of preterm infants. (See "Inherited hypokalemic salt-losing tubulopathies: Pathophysiology and overview of clinical manifestations", section on 'Bartter-like phenotype'.)

●Screen for maternal diabetes if not previously performed. (See "Gestational diabetes mellitus: Screening, diagnosis, and prevention".)

Congenital infection may be associated with maternal signs or symptoms of infection and/or fetal abnormalities (eg, hydrops, growth restriction, hepatosplenomegaly, cerebral ventriculomegaly, intracranial and intraabdominal calcifications, hyperechogenic fetal bowel, ascites). In the absence of maternal signs and symptoms or fetal findings (other than polyhydramnios), congenital infection (rubella, cytomegalovirus, toxoplasmosis, syphilis) is an unlikely cause of isolated polyhydramnios and we do not screen for it [19,51].

OUTCOME — Many idiopathic cases resolve spontaneously, especially if mild [1,52,53]. Transient cases generally have a benign maternal course, but have been associated with an increased risk for macrosomia [53].

In a meta-analysis (12 retrospective studies, 2392 idiopathic cases), the odds of the following outcomes were increased compared with pregnancies with normal AFV: neonatal death OR 8.7, fetal demise OR 7.6, macrosomia OR 2.9, malpresentation OR 2.7, cesarean birth OR 2.3, 5-min Apgar score <7 OR 2.2, neonatal intensive care unit admission OR 1.9 [54]. Limitations of the analysis included lack of subdivision for mild, moderate, or severe cases (although the majority were mild case); some studies included diagnoses from the early-second trimester and others from the third trimester; and different criteria were used for the diagnosis of polyhydramnios. A retrospective study that specifically addressed mild idiopathic polyhydramnios compared 204 such cases with 12,476 cases with normal amniotic fluid volume and demonstrated an increased risk of fetal demise (OR 3.38), 5-minute APGAR score <7 (OR 1.68), and LGA (OR 3.87) [55].

Persistent polyhydramnios has been associated with an increased risk of several adverse maternal and newborn outcomes in addition to the poor outcomes related to the associated fetal morphologic abnormalities [56-59]:

●Maternal respiratory compromise

●Prelabor rupture of membranes

●Preterm labor and birth

●Fetal malposition

●Macrosomia (potentially leading to shoulder dystocia)

●Umbilical cord prolapse

●Abruption (particularly upon membrane rupture)

●Longer second stage of labor

●Postpartum uterine atony

These complications increase the risk for cesarean birth and admission to a neonatal intensive care unit.

Maternal respiratory compromise, fetal malposition, cord prolapse, and postpartum uterine atony are related to uterine overdistention from excessive amniotic fluid volume (AFV).

Fetal/newborn prognosis — Preterm labor and preterm prelabor rupture of membranes can lead to spontaneous preterm birth. Preterm birth in affected pregnancies also may be caused by iatrogenic interventions. (See "Overview of short-term complications in preterm infants" and "Overview of the long-term complications of preterm birth" and "Preterm birth: Definitions of prematurity, epidemiology, and risk factors for infant mortality".)

The overall risk of fetal death and neonatal death appears to be increased in pregnancies with polyhydramnios compared with pregnancies with normal amniotic fluid, even after adjusting for confounders, such as congenital anomalies and maternal diabetes [7,60-64]. The relative risk appears to increase with increasing severity of polyhydramnios. The absolute risk of death depends upon the etiology. For example, the combination of a small for gestational age fetus and polyhydramnios has a particularly poor prognosis (including perinatal death) due to the high prevalence of fetal chromosomal and structural abnormalities in this setting [65,66].

Idiopathic polyhydramnios has also been associated with an increased risk of neonatal morbidity at term, especially neonatal respiratory morbidity [67]. A study on bronchopulmonary dysplasia (BPD) in preterm infant used a logistic regression model to evaluate different prenatal exposures in 1385 BPD cases and 3142 controls and demonstrated that polyhydramnios may be a clinical indicator of premature infants at increased risk for BPD [68]. These and other adverse sequelae associated with idiopathic polyhydramnios are likely related to underlying etiologies, such as malformations, genetic syndromes, and neurologic disorders, that were not identified before birth [69].

MANAGEMENT OF POLYHYDRAMNIOS IN SINGLETON PREGNANCIES — Management of twin pregnancies is reviewed separately. (See "Twin-twin transfusion syndrome: Screening, prevalence, pathophysiology, and diagnosis" and "Twin-twin transfusion syndrome: Management and outcome".)

Polyhydramnios with an identifiable etiology

●The specific underlying etiology of the polyhydramnios should guide antepartum fetal and maternal surveillance, intrapartum management, and timing of birth. (Refer to topics on specific etiologies.)

●For patients with severe symptomatic polyhydramnios, management of maternal symptoms is similar to that for patients with idiopathic polyhydramnios. (See 'Additional issues in patients with severe polyhydramnios' below.)

Idiopathic polyhydramnios — Management of idiopathic polyhydramnios depends upon the gestational age, severity, and presence of symptoms.

All patients — We order antepartum fetal monitoring in all patients with idiopathic polyhydramnios:

●For mild to moderate polyhydramnios, we obtain a biophysical profile (BPP, including the nonstress test [NST] component) upon diagnosis and then every 1 to 2 weeks until 37 weeks, and then weekly from 37 weeks to birth.

●For severe polyhydramnios, we obtain the BPPs (including NST) every week from diagnosis until birth. In interpreting the BPP score, clinicians should be cautious about conclusions of fetal well-being with a borderline score (6/8) since the two points for amniotic fluid volume (AFV) in these cases are not reassuring.

No randomized trials have evaluated whether pregnancies complicated by idiopathic polyhydramnios benefit from any method of antenatal surveillance. Although there are no data to suggest that such assessment decreases perinatal mortality, given the increased risk of fetal mortality in these cases (OR 7.6, 95% CI 2.5-23.4 in a meta-analysis [54]), we order antenatal fetal monitoring tests. The Society for Maternal-Fetal Medicine (SMFM) does not consider antenatal fetal surveillance mandatory in pregnancies with mild idiopathic polyhydramnios and no other indication for surveillance [42].

Additional issues in patients without severe polyhydramnios — Patients without severe polyhydramnios are not candidates for intervention as they typically do not experience severe symptoms related to polyhydramnios, pregnancy outcome may not be adversely affected, and there are no interventions that improve pregnancy outcome [42,70].

Additional issues in patients with severe polyhydramnios — Severe (amniotic fluid index [AFI] ≥35 cm or single deepest pocket [SDP] ≥16 cm) polyhydramnios may cause maternal shortness of breath, abdominal discomfort, and uterine contractions. The decision to intervene depends on symptom severity. Our approach is discussed below and shown in the algorithm (algorithm 1).

Asymptomatic patients and patients with mild symptoms — Intervention to reduce amniotic fluid is not indicated in asymptomatic patients or patients with mild shortness of breath, abdominal discomfort, and/or uterine irritability that is reasonably tolerable, as pregnancy outcome may not be adversely affected and there are no interventions that improve pregnancy outcome [42,70].

Patients with severe shortness of breath and/or abdominal discomfort

●For patients with severe polyhydramnios causing severe shortness of breath and/or abdominal discomfort (ie, significantly interfering with the patient's ability to conduct the normal activities of daily life), we suggest decompression amniocentesis (also called amnioreduction) to normalize fluid volume. The goal is to relieve the significant maternal discomfort and avoid iatrogenic preterm birth for maternal indications [70,71]. There is no evidence that the procedure prolongs gestation by reducing the risk of spontaneous preterm labor and birth. We also administer a course of antenatal betamethasone. The procedure for the initial and subsequent decompression amniocenteses is described below. (See 'Amnioreduction (decompression amniocentesis)' below.)

No randomized trials have directly compared amnioreduction with expectant management or indomethacin for management of polyhydramnios. In the largest series of amnioreduction for treatment of polyhydramnios (138 patients), 46 percent of patients required >1 procedure, the median duration from the first procedure until delivery was 26 days, and 4 percent of procedures were associated with unplanned preterm birth within 48 hours, which was the only complication in this series (no cases of chorioamnionitis or abruption) [70]. Although data on symptom relief were not collected, anecdotally, the authors felt that patients typically had a favorable response.

SMFM recommends considering amnioreduction for relief of severe maternal discomfort, dyspnea, or both in the setting of severe polyhydramnios, and has recommended not using indomethacin for the sole purpose of decreasing amniotic fluid in these cases because of concerns about medication-related neonatal complications [42].

Patients with preterm labor/frequent uterine contractility

●<32 weeks of gestation and not meeting symptom criteria for amnioreduction – For patients with preterm labor or distressing uterine irritability but without severe shortness of breath or abdominal discomfort necessitating amnioreduction, we give a short course (48 hours) of indomethacin alone to reduce contractile activity and potentially delay birth. An additional advantage of indomethacin is that it may reduce AFV. We also administer a course of antenatal betamethasone, given the risk of preterm birth.

●<32 weeks of gestation and meeting symptom criteria for amnioreduction – For patients <32 weeks who are undergoing amnioreduction because of severe shortness of breath or abdominal discomfort and who have periprocedural uterine contractions, we give a short course (48 hours) of indomethacin before and/or after the procedure to utilize both its tocolytic and therapeutic effects (reduce the rate of reaccumulation of amniotic fluid and recurrent polyhydramnios). Amnioreduction may also reduce uterine activity [72].

●≥32 and <34 weeks – We do not use indomethacin to treat preterm labor/bothersome uterine irritability at this gestational age because of the potential for adverse fetal/neonatal effects. We would use another tocolytic (eg, nifedipine or a beta-2-receptor agonist), if needed, to delay birth and enable a course of antenatal betamethasone.

●≥34 weeks – We do not use any tocolytic to treat preterm labor/bothersome uterine irritability in pregnancies ≥34 weeks of gestation. We would administer an initial course of betamethasone to pregnancies at 34+0 to 36+6 weeks of gestation at high risk for preterm birth within seven days, according to standard guidelines. (See "Antenatal corticosteroid therapy for reduction of neonatal respiratory morbidity and mortality from preterm delivery", section on '34+0 or more weeks'.)

Indomethacin dosing and side effects are discussed below. (See 'Indomethacin' below.)

Refractory symptoms — Amnioreduction should relieve maternal symptoms immediately, but amniotic fluid can reaccumulate within a few days to weeks.

●<34 weeks of gestation – For patients with severe symptoms due to recurrent polyhydramnios after an initial amnioreduction, we repeat amnioreduction. We also consider, on a case-by-case basis, another short course (48 hours) of indomethacin for those <32 weeks with persistent uterine irritability to take advantage of its favorable effects on both uterine activity and AFV in this setting [42].

●≥34 weeks of gestation – For patients with severe symptomatic polyhydramnios ≥34 weeks in whom amnioreduction has been unsuccessful because of rapid reaccumulation of fluid, we discuss preterm birth for relief of maternal discomfort and make this shared decision on a case-by-case basis.

Amnioreduction (decompression amniocentesis) — There is no consensus about how much amniotic fluid to remove, how rapidly to remove the fluid, or use of tocolytic medications and antibiotics. We do not use antibiotic prophylaxis and only initiate indomethacin as a tocolytic in patients with contractions.

●Technique – A common technique is to:

•Cleanse the site with a surgical scrub and then administer local anesthesia into the skin and subcuticular tissues.

•Under continuous ultrasound guidance to minimize fetal contact, insert an 18-gauge needle with the tip directed toward the fluid. It is often useful to insert the needle in a caudal direction with the hub of the needle positioned cranially so the needle can be advanced as the uterus becomes smaller with decompression.

•Attach hard-walled arterial line tubing with a three-way stopcock to the needle and connect to a vacuum suction bottle. The fluid may be suctioned directly into the container or, alternatively, removed with a 50 mL syringe under controlled suction, but this can be tedious when there is a lot of fluid.

•A reasonable guideline is to remove no more than 2.0 to 2.5 liters at one time and to remove the fluid no faster than 1000 mL over 20 minutes, although rates of 100 to 125 mL/minute have been reported [70].

•Terminate the procedure when the AFV is normalized (generally AFI 15 to 20 cm or maximum vertical pocket <8 cm) [39]. Sometimes, the procedure will need to be terminated early because of patient discomfort, a clogged needle, or membrane separation.

●Complications – Complication rates in small series are generally low, ranging from 1 to 10 percent of procedures. Complications include preterm labor and prelabor rupture of membranes, which are the most common complications, and less commonly abruption, intraamniotic infection, and hypoproteinemia [70,71,73,74].

●Postprocedure follow-up – Following amnioreduction, we monitor AFV every one to three weeks as indicated by the progression and severity of the amniotic fluid reaccumulation process.

●Repeat procedures – Repeat procedures can be performed at any interval. On average, two procedures at least a week apart are needed to reduce AFV chronically, although some patients require many more procedures [71,73]. One unusual case report described 12 amnioreductions over 12 weeks that removed a total of 21,600 mL of fluid; the infant was diagnosed with West syndrome at follow-up 16 months after birth [17].

Indomethacin — SMFM recommends not administering indomethacin for the sole indication of reducing amniotic fluid [42]. As noted above, in pregnancies <32 weeks of gestation with preterm labor/uterine irritability, we sometimes use a short course (48 hours) of indomethacin for its combined effects of tocolysis and reduction in AFV. Adverse fetal effects, including premature closure of the ductus arteriosus and renal impairment, are a concern when the drug is used for ≥3 days and when it is used at ≥30 weeks. (See 'Patients with preterm labor/frequent uterine contractility' above and 'Refractory symptoms' above.)

Maternal administration of prostaglandin synthetase inhibitors reduces AFV in pregnancies with normal or abnormal AFV at baseline. These drugs may stimulate fetal secretion of arginine vasopressin and facilitate vasopressin-induced renal antidiuretic responses and reduce renal blood flow, thereby reducing fetal urine flow. They also may impair production or enhance reabsorption of lung liquid [75].

●Dosing – Various indomethacin regimens have been used, but a common approach is an initial dose of 25 mg orally four times daily and limiting treatment to pregnancies <32 weeks and to a short course (48 hours) of therapy [76].

●Maternal and fetal side effects – Maternal side effects, such as nausea, esophageal reflux, gastritis, and emesis, have been studied primarily in patients receiving the drug for inhibition of preterm labor; the prevalence of side effects in this population is 4 percent. Platelet dysfunction may occur. Alterations in maternal cardiovascular physiology are minimal. (See "Nonselective NSAIDs: Overview of adverse effects".)

The primary fetal concern with use of indomethacin is constriction of the ductus arteriosus. This side effect is more likely when the duration of indomethacin exposure exceeds 72 hours and when gestational age is ≥32 weeks. Prolonged indomethacin use may also result in oligohydramnios and fetal/neonatal renal impairment.

Other possible fetal adverse effects include neonatal necrotizing enterocolitis and intraventricular hemorrhage, but these associations are more controversial. Effects of indomethacin on the fetus/neonate are discussed in more detail separately. (See "Inhibition of acute preterm labor", section on 'Fetal side effects'.)

Labor management — During labor, we check fetal position frequently to confirm maintenance of cephalic presentation. The excess amniotic fluid allows greater fetal mobility, so conversion to a breech, compound, or transverse presentation may occur. The fetal heart rate is monitored continuously as these pregnancies are at increased risk of abnormalities [77,78].

Membrane rupture — Spontaneous rupture of membranes can cause sudden severe uterine decompression with risk of cord prolapse or abruption. Prophylactic gradual abdominal or transcervical amnioreduction with a needle when the head is engaged may prevent these complications during labor. The risk of cord prolapse should be considered if membrane rupture at high station is being contemplated solely for uterine decompression. Controlled amniotomy in the operating room is performed by using a small gauge needle to puncture the fetal membranes in one or more places, while a second operator is stabilizing the fetus in longitudinal lie/cephalic presentation. This minimizes the risk of gushing amniotic fluid and allows for rapid cesarean birth in the event of cord prolapse. Similarly, the amniotomy should be performed between, not during, uterine contractions, if possible.

Timing of delivery — Although there is no absolute contraindication to use of oxytocin or prostaglandins for cervical ripening and labor induction in patients with polyhydramnios, these drugs should be used with caution. There is a marked increase in the incidence of postpartum hemorrhage related to atony in patients with polyhydramnios; use of uterine stimulants may increase this risk and that of amniotic fluid embolism [76,79]. However, we use prostaglandins for cervical ripening and oxytocin for induction, as clinically indicated. (See "Induction of labor: Techniques for preinduction cervical ripening" and "Induction of labor with oxytocin".)

Timing of delivery is influenced by the underlying etiology and the severity of polyhydramnios:

●Mild to moderate polyhydramnios – In patients with mild to moderate idiopathic polyhydramnios (table 2) and normal BPPs, we induce labor at 39+0 to 40+0 weeks of gestation as the risk of fetal death appears to increase significantly at term [64]. The American College of Obstetricians and Gynecologists/SMFM recommends birth at 39+0 to 40+6 weeks for patients with mild idiopathic polyhydramnios [80].

●Severe polyhydramnios – In patients with severe idiopathic polyhydramnios, we offer induction of labor at 37+0 weeks to minimize the risk of umbilical cord prolapse and/or abruption in the event of spontaneous prelabor rupture of membranes. We offer earlier delivery on a case-by-case basis to patients between 34+0 and 37+0 weeks whose symptoms are intolerable and who have not responded to amnioreduction procedures.

Delivery at a tertiary center is recommended for patients with severe idiopathic polyhydramnios since clinically important fetal abnormalities may not have been identified prenatally.

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: Oligohydramnios and polyhydramnios".)

SUMMARY AND RECOMMENDATIONS

●Pathogenesis and etiology – Polyhydramnios may be idiopathic or associated with a variety of fetal disorders (table 1). Decreased fetal swallowing or increased fetal urination is often the underlying mechanism for increased amniotic fluid volume (AFV). The most common associated conditions are fetal malformations and/or genetic disorders, maternal diabetes mellitus, multiple gestation, and fetal anemia. Bartter syndrome is a rare cause. (See 'Pathogenesis' above and 'Conditions associated with polyhydramnios' above.)

●Diagnosis – In patients with a qualitative impression of polyhydramnios, we suggest performing a quantitative measurement. We use single deepest pocket (SDP) ≥8 cm or amniotic fluid index (AFI) ≥24 cm to define polyhydramnios. Quantitative indices are standardized and provide a measurement that can be followed on serial examinations, even though sensitivity and positive predictive value are suboptimal. (See 'Diagnosis' above.)

●Postdiagnostic evaluation (see 'Postdiagnostic evaluation' above)

•Detailed sonographic evaluation to look for fetal anomalies and/or hydrops

•Laboratory evaluations depend upon sonographic findings and may include screening for gestational diabetes, testing for fetomaternal hemorrhage if fetal anemia is suspected, maternal serology to determine exposure to infectious agents (eg, syphilis, parvovirus, cytomegalovirus, toxoplasmosis, rubella), and appropriate tests for hereditary anemias (eg, alpha-thalassemia) or inborn errors of metabolism. (See 'Postdiagnostic evaluation' above.)

•We offer fetal microarray analysis in cases of severe polyhydramnios or if there are associated anatomic anomalies, especially if the results will affect management. Amniotic fluid biochemical analyses can help in the diagnosis of esophageal atresia and Bartter syndrome.

●Outcome – The outcome of pregnancies complicated by polyhydramnios varies according to the severity and underlying etiology of the excessive fluid accumulation. Possible complications include maternal respiratory compromise, preterm labor, prelabor rupture of membranes, fetal malposition, abruption, umbilical cord prolapse, fetal or neonatal death, and/or postpartum uterine atony. (See 'Outcome' above.)

●Initial management – We limit treatment of idiopathic polyhydramnios to singleton pregnancies with severe polyhydramnios (AFI ≥35 cm or SDP ≥16 cm) and severe symptoms (ie, significantly interfering with the patient's ability to conduct the normal activities of daily life).

•For asymptomatic patients or patients with mild shortness of breath, abdominal discomfort, and/or uterine irritability that is reasonably tolerable, we suggest avoiding intervention to reduce amniotic fluid (Grade 2C). (See 'Asymptomatic patients and patients with mild symptoms' above.)

•For patients with severe polyhydramnios causing significant shortness of breath and/or abdominal discomfort, we suggest amnioreduction (decompression amniocentesis) rather than indomethacin to normalize fluid volume (Grade 2C). Indomethacin can have adverse fetal effects. We also administer a course of antenatal betamethasone. (See 'Patients with severe shortness of breath and/or abdominal discomfort' above and 'Indomethacin' above.)

•For patients <32 weeks who are undergoing amnioreduction and have periprocedural uterine contractions, we suggest a short course (48 hours) of indomethacin before and/or after the procedure (Grade 2C). This utilizes both its tocolytic and therapeutic effects (reduces the rate of reaccumulation of amniotic fluid and recurrent polyhydramnios). (See 'Patients with preterm labor/frequent uterine contractility' above.)

•For patients <32 weeks with severe polyhydramnios and preterm labor/bothersome uterine irritability but without significant shortness of breath or abdominal discomfort necessitating amnioreduction, we suggest a short course (48 hours) of indomethacin alone to reduce contractile activity and potentially delay delivery (Grade 2C). An additional advantage of indomethacin is that it may reduce amniotic fluid volume (AFV). We also administer a course of antenatal betamethasone given the risk of preterm birth. (See 'Patients with preterm labor/frequent uterine contractility' above.)

●Management of refractory idiopathic polyhydramnios (see 'Refractory symptoms' above)

•For patients <34 weeks with severe symptoms due to recurrent polyhydramnios after an initial amnioreduction, we perform repeat amnioreduction and consider, on a case-by-case basis, another short course (48 hours) of indomethacin to those <32 weeks with persistent uterine irritability to take advantage of its favorable effects on both uterine activity and AFV in this setting.

•For patients with severe symptomatic polyhydramnios at ≥34 weeks in whom amnioreduction has been unsuccessful because of reaccumulation of fluid, we discuss preterm delivery for relief of maternal discomfort and make this shared decision on a case-by-case basis.

●Timing of delivery – We deliver patients with mild idiopathic polyhydramnios 39+0 to 40+0 weeks. Timing in other cases depends on the etiology and severity. (See 'Timing of delivery' above.)

●Intrapartum management – During labor, fetal position should be checked frequently as the excess amniotic fluid allows greater fetal mobility, so conversion to a breech, compound, or transverse presentation may occur. Spontaneous rupture of membranes can cause sudden severe uterine decompression with risk of cord prolapse or abruption. Prophylactic gradual abdominal or transcervical amnioreduction with a needle when the head is engaged may prevent these complications during labor. (See 'Labor management' above.)