Unengaged vertex in nulliparous women in active labor. A risk factor for cesarean delivery.

OBJECTIVE To compare the route of delivery among nulliparous parturients with and without an engaged vertex in the early, active phase of labor. METHODS Prospectively, the position of the fetal head was ascertained among nulliparous women at 37 weeks' gestation or more in early, active labor (cervical dilation > or = 4 cm with adequate contractions). Sixteen variables, including maternal demographics, obstetric complications and intrapartum course, were examined using chi 2 and logistic regression analysis. RESULTS Among the 77 patients, 33 (42.8%) had an unengaged vertex and 44 (57.2%) had an engaged vertex in active labor. Of the 22 cesarean deliveries for arrest disorder, 2 were in the engaged and 20 in the unengaged group (P < .001). The mean birth weight was similar among those who had vaginal (3,211 +/- 416 g) and cesarean delivery (3,400 +/- 489 g, P = .08). Univariate analysis indicated that chorioamnionitis (relative risk [RR] 2.6, 95% confidence interval [CI] 1.4-4.9) and unengaged vertex (RR 13.3, CI 3.3-53.0) were associated with cesarean delivery for arrest disorders. When entered into a multiple logistic model, only unengagement was a risk factor for cesarean delivery. The following were not associated with cesarean delivery: maternal demographics, gestational age, estimate of fetal weight, presence or absence of meconium, preeclampsia, diabetes mellitus, private obstetric care or use of epidural anesthesia. CONCLUSION Among nulliparous parturients, an unengaged vertex is a significant risk factor for cesarean delivery for arrest disorders.