Intrapartum amniotic fluid index: a poor predictor of abnormal fetal size.
OBJECTIVE
Using receiver-operating characteristic (ROC) curves, we tried to determine the diagnostic threshold of amniotic fluid index (AFI) that will identify abnormal fetal size (birth weights under 2500 g or at least 4000 g) at 37 weeks or beyond.


METHODS
We analyzed prospectively over 2 years all parturients with intact membranes and known AFI 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 error of the mean [SE]) under the curves were calculated. P < .05 was considered significant.


RESULTS
Of the 1038 subjects meeting study criteria, 3.6% and 11.5% gave birth to infants who were small for gestational age (SGA) or macrosomic, respectively. Overall, 28.7% had oligohydramnios (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 under ROC curves are not significantly different from the area under the nondiagnostic 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.


CONCLUSIONS
Intraparterium AFI appears to be a poor screening test to identify risk for delivery of SGA or macrosomic fetus.
Hendrix
N W
NW
Department of Obstetrics and Gynecology at Medical College of Georgia, Augusta, USA.
Chauhan
S P
SP
Magann
E F
EF
Martin
J N
JN
Morrison
J C
JC
Devoe
L D
LD
D000328:Adult; D000653:Amniotic Fluid / Q000502:physiology; D000704:Analysis of Variance; D001724:Birth Weight; D005260:Female; D005333:Fetus / Q000033:anatomy & histology*; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D016104:Oligohydramnios / Q000150:complications; D011247:Pregnancy; D011446:Prospective Studies; D012372:ROC Curve