Idiopathic Polyhydramnios and Pregnancy Outcome: Systematic Review and Meta-analysis
Authors: Pagan M. , Magann E. F. , Rabie N. , Steelman S. C. , Hu Z. , Ounpraseuth S. 
Published: September 2023

Amniotic fluid volume (AFV) is examined via ultrasound often several times in pregnancy and can be an indicator of the overall health of a fetus. However, disorders of amniotic fluid can arise without complications for the fetus; excess of amniotic fluid without any accompanying fetal conditions is referred to as idiopathic polyhydramnios. Previous research has shown conflicting results with regard to outcomes related to idiopathic polyhydramnios, with some finding it increases adverse outcomes and others reporting an increase in adverse outcomes only in moderate or severe cases. This study is a systematic review and meta-analysis meant to assess the relationship between idiopathic polyhydramnios and perinatal outcomes for singleton pregnancies.

Eligibility criteria included studies that had a control group with normal AFV and defined polyhydramnios as an amniotic fluid index of 24 cm or greater or a single deepest pocket of 8 cm or greater. Similar methods of defining polyhydramnios were considered as long as they were evidence-based. Studies with known causes of polyhydramnios were excluded to ensure cases analyzed for this study were idiopathic. The primary outcome was intrauterine fetal demise, with secondary outcomes of neonatal death, neonatal intensive care unit (NICU) admission, macrosomia, 5-minute Apgar score, malpresentation, and cesarean delivery.

Final review and analysis included 12 articles, with a total of 2392 patients with idiopathic polyhydramnios and 160,135 patients with normal AFV. Risk of bias was determined to be low for these studies, although the comparability was not well-defined. Analysis for the primary outcome included 8 of the 12 studies and showed that the risk of intrauterine fetal demise was increased in those with idiopathic polyhydramnios (odds ratio [OR], 7.64; 95% confidence interval [CI], 2.50–23.38).

Secondary outcome analysis for neonatal death showed that individuals with polyhydramnios were 8.68 times more likely to experience neonatal death than controls (95% CI, 2.91–25.87). Examining other secondary outcomes, the association between NICU admission and idiopathic polyhydramnios showed that patients with polyhydramnios were more likely to be admitted to the NICU (OR, 1.94; 95% CI, 1.45–2.59). When assessing 5-minute Apgar scores, results showed that individuals with polyhydramnios were more likely to have an Apgar score of less than 7 (OR, 2.21; 95% CI, 1.34–3.62). In addition, rates of cesarean delivery were significantly higher with idiopathic polyhydramnios (OR, 2.31; 95% CI, 1.79–2.99), as was macrosomia (OR, 2.93; 95% CI, 2.39–3.59). Malpresentation was also higher in the polyhydramnios group than in the control group (OR, 2.73; 95% CI, 2.06–3.61).

The authors of this meta-analysis conclude that in pregnancies with idiopathic polyhydramnios, there is an elevated risk of both intrauterine fetal demise and neonatal death. In addition, all other negative pregnancy outcomes analyzed were more common in pregnancies affected by idiopathic polyhydramnios. One limitation of this review is the heterogeneity inherent in analyzing many studies with different sample characteristics and different analysis methods. Although efforts were made to reduce bias, there is some inherent bias that cannot be accounted for completely. Further research is needed to fully characterize the clinical implications of the increased risk for adverse pregnancy outcomes shown here. This study also showed an increased risk based on the current clinical threshold for polyhydramnios, but more data are needed on accurate AFV thresholds and the clinical implications stemming from various thresholds.