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

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.

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.

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).

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.