Antenatal testing among 1001 patients at high risk: the role of ultrasonographic estimate of amniotic fluid volume.

OBJECTIVE: Our goal was to compare the accuracy of the amniotic fluid index and the 2-diameter pocket technique with respect to accuracy in predicting an adverse pregnancy outcome among patients at high risk undergoing antenatal testing.

STUDY DESIGN: All women with high-risk pregnancies and intact membranes who underwent antenatal testing during an 18-month period were prospectively enrolled. Ultrasonographic estimates of amniotic fluid volume were performed by means of the amniotic fluid index and the 2-diameter pocket technique. Relative risks with 95% confidence intervals and receiver operator characteristic curves were calculated for patients with an ultrasonographic estimate of oligohydramnios (amniotic fluid index of 5 cm or 2-diameter pocket of >15 cm2). Outcome variables studied were intrapartum and neonatal complications.

RESULTS: Among 1001 patients the mean (+/-SD) amniotic fluid index was 10.5 +/- 5 cm and the mean (+/-SD) 2-diameter pocket was 18.7 +/- 13.6 cm2. Significantly more patients (46%) were considered to have oligohydramnios according to the 2-diameter pocket criteria than according to the amniotic fluid index (21%, P <.0001, relative risk 1.7, 95% confidence interval 1.5-1.8). No significant differences in the incidences of nonreactive nonstress test results, meconium-stained amniotic fluid, cesarean delivery for fetal distress, low Apgar scores, or infants with cord pH of <7.10 were observed between the oligohydramnios and normal amniotic fluid groups (P >.05) when assessed by relative risk with confidence interval and by receiver operator characteristic curves.

CONCLUSIONS: Current ultrasonographic measurements with the amniotic fluid index and the 2-diameter pocket technique are poor diagnostic tests to determine whether a patient is at high risk for an adverse perinatal outcome.