Efficacy of the fetal-pelvic index in nulliparous women at high risk for fetal-pelvic disproportion.

Abstract

The null hypothesis of this study is that the fetal-pelvic index will not determine the presence or absence of fetal-pelvic disproportion in 137 nulliparous women at high risk for fetal-pelvic disproportion. This study was undertaken by comparing the blinded fetal-pelvic index values and two other methods of identifying fetal-pelvic disproportion, ultrasonography-derived estimated fetal weight greater than or equal to 4000 gm and Mengert's index, to delivery outcomes in 137 nulliparous women at high risk for fetal-pelvic disproportion. After adequate labor trials, 55 of 73 patients who required operative intervention had a positive fetal-pelvic index (sensitivity = 75%). Seventeen of the 18 patients with a false-negative fetal-pelvic index value had persistent malpositions (15 occipitoposterior, 1 occipitotransverse, and 1 face presentation). Spontaneous vaginal deliveries occurred in 64 patients with 62 of them having a negative fetal-pelvic index (specificity 97%). The overall predictability of the fetal-pelvic index in this patient population was 85% and the positive predictability was 96%. However, neither ultrasonography-derived estimated fetal weight nor x-ray pelvimetry, when used alone, accurately detected the presence or absence of fetal-pelvic disproportion in nulliparous women at high risk for the condition. The fetal-pelvic index is efficacious in determining the presence or absence of fetal-pelvic disproportion in nulliparous women at high risk for the condition.