Abnormal amniotic fluid volume is associated with neonatal respiratory outcomes in the late preterm period

Introduction The clearance of fluid from the fetal lungs is important for a neonate to successfully transition to breathing room air. We hypothesized that abnormal amounts of amniotic fluid (AF; either oligohydramnios [OLIGO] or polyhydramnios [POLY]) would increase the risk of neonatal respiratory morbidity. Methods This study is a secondary analysis of a multicenter randomized controlled trial. Patients were included if they were of late preterm gestation (34w0d‐36w5d) and had documented AF volume. Two exposures were separately investigated—OLIGO (maximum vertical pocket [MVP] <2 cm or AF index [AFI] <5 cm) and POLY (MVP > 8 cm or AFI > 24 cm). The primary outcome was a composite of neonatal respiratory support, including continuous pulmonary airway pressure or high flow nasal cannula for ≥2 h, or oxygen support (fraction of inspired oxygen ≥30%) for ≥4 h within the first 72 h of life. Secondary outcomes were major respiratory morbidity, respiratory distress syndrome (RDS), transient tachypnea of the newborn (TTN), and neonatal intensive care unit admission. Statistical analysis was performed with Student's t‐test, Wilcoxon rank sum, and chi‐square analyses, followed by logistic regression modeling to adjust for baseline differences between groups. Results Our study included 2792 subjects (normal fluid: 2590, OLIGO: 172, and POLY: 29). The OLIGO subjects were less likely to require neonatal respiratory support (6.4% vs. 12.5%, p = 0.02) or experience major respiratory morbidity (4.7% vs. 10.0%, p = 0.02), compared to normal AF controls. After controlling for baseline characteristics, OLIGO was still associated with less use of neonatal respiratory support (adjusted odds ratio [aOR], 0.52; 95% confidence interval [CI], 0.28–0.97). The primary outcome did not differ between the POLY group and the control group (20.7% vs. 12.5%, p = 0.18). However, after controlling for baseline characteristics, POLY was significantly associated with TTN (aOR, 2.80; 95% CI, 1.03–7.62) and use of mechanical ventilation (aOR, 4.22; 95% CI, 1.19–14.95). Conclusion AF status in the late preterm period is associated with neonatal respiratory outcomes—OLIGO is associated with a lower requirement for neonatal respiratory support, while POLY is associated with TTN and the need for mechanical ventilation.