Ultrasound assessment of amniotic fluid volume: a comparison of the single deepest pool and amniotic fluid index to predict perinatal morbidity.

Abstract

The ability of the amniotic fluid index and the single deepest pool to predict perinatal morbidity was compared in 291 high-risk singleton pregnancies without ruptured membranes or fetal renal abnormalities. A poor outcome was defined as a birth weight < -2 standard deviations, emergency Cesarean section for fetal heart rate abnormalities in labor, 5-minute Apgar score < 7, umbilical venous pH at delivery < 7.15 and admission to the special care baby unit. At least one of these parameters occurred in 71 (24%) of the 291 pregnancies. Oligohydramnios (an amniotic fluid index <or= 5 cm) occurred in 19 (6.5%) of the 291 pregnancies; this group was more likely to have a poor outcome than those with an amniotic fluid index > 5 cm (chi(2) = 2.41, p = 0.02). There was a significant correlation between amniotic fluid index and single deepest pool measurements (r = 0.83, n = 291, p < 0.0001). At the recommended cut-off values, the single deepest pool and the amniotic fluid index had sensitivities of 7% and 13%, respectively and specificities of 96% and 95% for predicting perinatal morbidity. Receiver operating characteristic curve analysis showed that these poor results were not the result of the cut-off values chosen and that the performances of the amniotic fluid index and single deepest pool were similar.