Efficacy of the fetal-pelvic index as a predictor of fetal-pelvic disproportion in women with abnormal labor patterns that require labor augmentations.

The fetal-pelvic index, which compares fetal head and abdomen circumferences with respective maternal inlet and midpelvic circumferences, was introduced in 1986 as a means of identifying the presence or absence of fetal-pelvic disproportion. In this study the efficacy of the fetal-pelvic index was evaluated in 46 patients with abnormal labor patterns that required labor augmentations and was compared with that of two other means (Colcher-Sussman x-ray pelvimetry and ultrasonographically derived estimated fetal weight greater than or equal to 4000 gm). Of the 24 women who required operative intervention (19 cesarean sections and five operative vaginal procedures), 17 had positive fetal-pelvic index values (sensitivity = 0.71). Six of the seven fetuses of patients with false-negative fetal-pelvic index values persisted in an occipitoposterior presentation, and these patients failed to progress in labor. Of the 22 patients in whom vaginal deliveries were spontaneous, 21 had negative fetal-pelvic index values (specificity = 0.95). Of the 18 women with positive fetal-pelvic index values, 17 required operative intervention (positive predictability = 0.94). In contrast, when used alone, neither x-ray pelvimetry nor ultrasonographically derived estimated fetal weight greater than or equal to 4000 gm provided accurate identification of fetal-pelvic disproportion.