Station at onset of active labor in nulliparous patients and risk of cesarean delivery

Objective: To determine whether term nulliparas with an unengaged vertex pr esentation at onset of active labor have a higher risk for cesarean deliver y. Methods: A retrospective cohort of 1250 randomly chosen nulliparous patient s at 37-42 weeks' gestation who delivered between 1988 and 1989 were select ed. Four hundred forty-seven patients were excluded because of nonvertex pr esentation, cesarean delivery before active phase of labor, multiple gestat ion, delivery at less than 37 weeks' or greater than 42 weeks' gestation, i nduction of labor, or missing charts. For the purpose of this study, active labor was defined as regular contractions with cervical dilatation of at l east 3 cm. The station at onset of active labor was recorded. Engagement wa s considered to be at station 0 or below. Results: Of the 803 patients in the study group, 567 presented unengaged an d 236 patients presented engaged. The cesarean rates differed significantly between the two groups: 14% of those unengaged compared with 5% of those e ngaged (chi(2) = 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 on set of active labor delivered vaginally. Engaged vertex at the onset of act ive labor was associated with a lower risk of cesarean delivery. (C) 1999 b y The American College of Obstetricians and Gynecologists.