Objective: To determine whether term nulliparas with an unengaged vertex presentation at onset of active labor have a higher risk for cesarean delivery.
Methods: A retrospective cohort of 1250 randomly chosen nulliparous patients at 37–42 weeks' gestation who delivered between 1988 and 1989 were selected. Four hundred forty-seven patients were excluded because of nonvertex presentation, cesarean delivery before active phase of labor, multiple gestation, delivery at less than 37 weeks' or greater than 42 weeks' gestation, induction of labor, or missing charts. For the purpose of this study, active labor was defined as regular contractions with cervical dilatation of at least 3 cm. The station at onset of active labor was recorded. Engagement was considered to be at station 0 or below.
Results: Of the 803 patients in the study group, 567 presented unengaged and 236 patients presented engaged. The cesarean rates differed significantly between the two groups: 14% of those unengaged compared with 5% of those engaged (χ2 = 11.9, P < .001). After adjusting for confounding variables, engagement at the time of onset of active labor was associated with lower risk of cesarean delivery (odds ratio .512, 95% confidence interval .285, .922).
Conclusion: Eighty-six percent of nulliparas with an unengaged vertex at onset of active labor delivered vaginally. Engaged vertex at the onset of active labor was associated with a lower risk of cesarean delivery.
In attempting to optimize patient management and identify women at risk for cesarean delivery, a few investigators have studied the impact of an unengaged vertex at the time of active labor on the rate of cesarean.1–5 Gabbe et al6 state that engagement often occurs before the onset of true labor, especially in nulliparas. Can engagement, then, be used as another clinical indicator for increased incidence of cesarean delivery in nulliparas?
Engagement has been defined as the stage at which the widest part of the fetal head has passed through the pelvic inlet.7 It refers to the descent of the biparietal plane of the fetal head to a level below that of the pelvic inlet. Williams7 states further that in nulliparas, engagement occurs commonly during the last few weeks of pregnancy. Friedman and Sachtleben1 found in their series of studies that there was a significant association between higher station at the onset of labor and the incidence of fetopelvic disproportion. The incidence of a prolonged latent phase, primary dysfunctional labor, and secondary arrest of dilatation all decreased with a lower station at the time of admission to labor and delivery; their combined incidence decreased from 20.9% above station +1 to 11.4% below +1 station.1 Friedman and Sachtleben1 state that engagement of the fetal presenting part in nulliparas is related to delivery outcome, the incidence of cesarean delivery with unengaged vertex being six to eight times that of patients with engaged fetuses. In their subsequent study of 253 nulliparas, they found arrest of descent associated with fetopelvic disproportion in 52%.2 Those with arrest of descent showed deviations from normal, including prolongation of each of the phases of labor and slowing of the maximum slopes of dilatation and descent. Labor progression was also related to station of the fetal presenting part at the time of arrest. The higher the station, the slower and more protracted a course of labor.2
This study presents findings from a cohort of 1250 nulliparous patients in which engagement of the fetal vertex at the time of onset of active labor and its relation to cesarean delivery were investigated.
Eighty-six percent of nulliparas with unengaged fetal heads at onset of active labor delivered vaginally.
Department of Gynecology & Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Address reprint requests to: Daniel Roshanfekr, MD, St. Vincent's Medical Center, 153 West 11th Street, Smith 9, New York, NY 10011
Received June 15, 1998. Received in revised form September 9, 1998. Accepted September 17, 1998.