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362: Assessing the optimal definition of oligohydramnios associated with adverse pregnancy outcomes

      Objective

      The optimal definition of oligohydramnios associated with adverse pregnancy outcomes is still unclear. Our objective was to compare the use of amniotic fluid index (AFI) < 5 cm to < the 5th percentile for gestational age in predicting adverse perinatal outcomes.

      Study Design

      A retrospective cohort study of pregnancies presenting to our prenatal ultrasound units from 1998-2008. Study subjects were identified by AFI < 5 cm and < 5th percentile for gestational age. The primary outcome measure was admission to the neonatal intensive care unit (NICU). Secondary outcomes included length of hospital stay, cesarean delivery, respiratory distress and Apgar scores. Relative risks were calculated for each outcome measure. The screening efficiency of each criteria of oligohydramnios for the primary outcome was determined. McNemar's test was used to compare the two criteria.

      Results

      17, 887 patients had complete information for analysis. There were 145 NICU admissions among the 904 patients with AFI < 5 cm (RR 2.2, [95%CI 1.88-2.58]) compared to 235 among the 1429 patients with AFI < 5th percentile for gestational age (RR 2.37, [95%CI 2.08-2.69]). For pregnancies with AFI > 5 cm but < 5th percentile for gestational age the RR for NICU admission was 2.30 (95%CI 1.89-2.80). There was a significant difference between the two criteria for oligohydramnios in predicting NICU admission (McNemar 2 p<0.001). The sensitivity and specificity for NICU admission utilizing AFI < 5 was 10.9% (95%CI 9.3-12.7) and 95.2% (95%CI 94.9-95.5) compared to 17.6% (95%CI 15.6-19.8) and 92.5% (95%CI 92.1-92.9) for < 5th % for gestational age.

      Conclusion

      Oligohydramnios defined as AFI < 5th percentile better predicts fetuses at risk for adverse perinatal outcome compared to AFI < 5 cm. Pregnancies with AFI > 5 cm but < the 5th percentile for gestational age are still at an increased risk for NICU admission.