An amniotic fluid index ≤ 5 cm within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess

Objective: To determine if an amniotic fluid index (AF1) ≤ 5.0 cm within 7 days of delivery in the third trimester is associated with decreasing umbilical arterial pH and base excess. Study Design: Case for this retrospective cohort study were all pregnancies ≥26 weeks with infact membranes and an AFI ≤ 5.0 cm within 7 days of delivery between 11/99 and 7/02. Multiple gestations, aneuploid, and anomalous fetuses were exclude. Controls with an AFI ≥ 5.0 cm within 7 days of delivery were metahed to each case within 1 week by gestational age. For a control group with a mean ± SD unbilical arterial pH of 7.26±0.07 and α = 0.05, a sample size of 100 would have a power of 99% to detect a difference with a study group whose mean was 7.20. Data were compared using paired Student's t-test, Mann-Whitney, Fisher's exact χ₂ and risk ratios with 95% confidence intervals. Results: In all, 131 neonates an AFI ≤ 5.0 cm were matched to 131 controls with an AFI > 5 cm. There was no diffence in gestational age (37.6±3.0, 37.7±3.0 weeks) or birth weight (2897±810, 2762±788 g). There was no difference in umbilical artery pH (7.25±0.07, 7.26±0.07) or base excess (-3.32±2.59, -2.83±2.45 mmol/l), even in small for gestational age (SGA) infants in both groups. There was no difference in the number of SGA neonates, 5-minute Apgar <7, respiratory distress syndrome, necrotizing entercolitis, or neurologic morbidity. Linear regrission showed no correlation between AFI and either umbilical arterial pH (r = -0.00047, SE = 0.001, p = 0.63) or base excess (r = -0.00047, SE = 0.001, p = 0.63) or base excess (r = -0.29, SE = 0.037, p = 0.428). Conclusion: An AFI ≤ 5.0 cm measured within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess.