INTRAPARTUM AMNIOTIC-FLUID INDEX - A POOR PREDICTOR OF ABNORMAL FETALSIZE

Objective: Using receiver-operating characteristic (ROC) curves, we tr ied to determine the diagnostic threshold of amniotic fluid index (AFI ) that will identify abnormal fetal size (birth weights under 2500 g o r at least 4000 g) at 37 weeks or beyond. Methods: We analyzed prospec tively over 2 years all parturients with intact membranes and known AF I in early labor. Patients with the following conditions were excluded : pregestational or gestational diabetes, known anomalies, and preterm labor. Two ROC curves were constructed, and the areas (+/- standard e rror of the mean [SE]) under the curves were calculated. P < .05 was c onsidered significant. Results: Of the 1038 subjects meeting study cri teria, 3.6% and 11.5% gave birth to infants who were small for gestati onal age (SGA) or macrosomic, respectively. Overall, 28.7% had oligohy dramnios (AFI at most 5.0 cm) and 3.6% had hydramnios (AFI at least 24 .0 cm). Small for gestational age was more common in patients with AFI at most 5.0 cm (6.4%) than in those with adequate fluid (AFI 5.1-23.9 ; 2.5%), or hydramnios (2.7%; P = .012). Macrosomic newborns were less likely to be born to women with oligohydramnios (7.7%) than to those with adequate amniotic fluid (13.1%) or hydramnios (13.5%). Areas unde r ROC curves are not significantly different from the area under the n ondiagnostic line, indicating that AFI (0-34 cm) cannot differentiate between newborns under 2500 g and at or over 2500 g or under 4000 and at or more 4000 g. Conclusion: Intraparterium AFI appears to be a poor screening test to identify risk for delivery of SGA or macrosomic fet us. (Obstet Gynecol 1998;92:823-7. (C) 1998 by The American College of Obstetricians and Gynecologists.).