Polyhydramnios and Adverse Perinatal Outcome

Abstract

Polyhydramnios complicates 1% to 3% of all pregnancies, and approximately 50% to 60% of cases are idiopathic. Although many fetal and maternal causes of polyhydramnios are known, idiopathic polyhydramnios is defined as that with no identifiable etiology. Amniotic fluid is commonly assessed using the amniotic fluid index (AFI), with polyhydramnios defined as an AFI of 24 cm or greater or 25 cm or greater, which is in the 95th or 97.5th percentile in normal singleton pregnancies. Polyhydramnios is subdivided into mild (24–30), moderate (30.1–35), and severe (AFI > 35). This retrospective cohort study was performed to reevaluate the cutoff point for polyhydramnios and identify a specific value associated with an increased risk for adverse outcomes. All patients enrolled had a sonographic assessment during pregnancy, and all had a singleton fetus at 20 weeks’ gestation or later with an AFI of greater than 10 cm. The patients were stratified into 5 groups according to the AFI: 10 to 19, 20 to 23, 24 to 27, 28 to 31, and 32 or greater. The group with AFI of less than 20 cm was the comparison group. Pregnancy characteristics, complications, and perinatal outcomes were compared among the groups. A total of 14,813 deliveries were enrolled: 9974 (67.3%) had 10 to 19, 2771 (18.7%) had 20 to 23, 1315 (8.8%) had 24 to 27, 494 (3.3%) had 28 to 31, and 260 (1.7%) had AFI of 32 or greater. Preterm labor, placental abruption, cesarean delivery, and malpresentation were more prevalent in a linear fashion as the AFI increased, with the highest prevalence in the group with AFI of 32 or greater. A nonlinear but significant difference between the groups was observed for prior cesarean delivery, gestational diabetes mellitus, postterm pregnancies, and macrosomia. With these complications, the prevalence increased as AFI increased up to an AFI of 31, with a relative decrease in the group with AFI of 32 or greater. A significantly increased rate of perinatal mortality was noted as AFI increased. The rate of low Apgar scores at 1 and 5 minutes was significantly higher and fetal pH tended to be lower in the groups with increased AFI. An Apgar score of less than 7 at 1 and 5 minutes showed a linear association with increased AFI. Three multiple logistic regression models using preterm labor, Apgar of less than 5 at 7 minutes, and perinatal mortality were constructed. All models exhibited a linear increase in the risk for adverse perinatal outcome with increasing AFI. The main finding of the study is the increased adverse perinatal outcome as AFI rises in a dose-response manner from AFI of greater than 20. The widely accepted cutoff for polyhydramnios is AFI of greater than 24, with established associations between polyhydramnios and adverse perinatal outcomes. A diagnosis of polyhydramnios requires additional evaluation to detect fetal anatomic or chromosomal anomalies or maternal conditions such as diabetes. The accepted definition of polyhydramnios as AFI of greater than 24 should be further reevaluated.