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 antena tal testing. STUDY DESIGN: All women with high-risk pregnancies and intact membranes who underwent antenatal testing during an 18-month period were prospectively e nrolled. 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 characte ristic curves were calculated for patients with an ultrasonographic estimat e of oligohydramnios (amniotic fluid index of less than or equal to 5 cm or 2-diameter pocket of less than or equal to 15 cm(2)) versus normal fluid l evel (amniotic fluid index of >5 cm or 2-diameter pocket of >15 cm(2)). Out come 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 cm(2). S ignificantly more patients (46%) were considered to have oligohy dramnios a ccording to the 2-diameter pocket criteria than according to the amniotic f luid 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 a ssessed 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 dete rmine whether a patient is at high risk for an adverse peri natal outcome.