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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 (AFI) r5.0 cm within 7 days of delivery in the third trimester is associated with decreasing umbilicalarterial pH and base excess.

STUDY DESIGN: Cases for this retrospective cohort study were all pregnancies ≥26 weeks with intact 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 excluded. Controls with an AFI >5.0 cm within 7 days of delivery were matched to each case within 1 week by gestational age. For a control group with a mean±SD umbilical 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 with an AFI ≤5.0 cm were matched to 131 controls with an AFI >5 cm. There was no difference 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 enterocolitis, or neurologic morbidity. Linear regression showed no correlation between AFI and either umbilical arterial pH (r=−0.00047, SE=0.001, p=0.63) or base excess (r=−0.029, 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.To determine if an amniotic fluid index (AFI) ≤5.0 cm within 7 days of delivery in the third trimester is associated with decreasing umbilical arterial pH and base excess.

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Driggers, R., Holcroft, C., Blakemore, K. et al. 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. J Perinatol 24, 72–76 (2004).

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