((เบนจี้))) In the present investigation of 1,347 nulliparas, cesarean delivery rates vis-à-vis latent phase durations were intermediate between the two above studies. For example, in this study, women with latent-phase durations of at least 12 hours had a 61% cesarean delivery rate, as compared with 87% in the Rouse study and 41% in the Simon and Grobman study. Maternal infection rates were comparable, and, similar to the increased rate of postpartum hemorrhage in the Simon and Grobman study, the rate of uterine atony, but not blood transfusion, was increased in the present investigation as the duration of the latent phase increased. In all three studies, failure to exit the latent phase after 12 hours of oxytocin and ruptured membranes was uncommon: 4%,6 17%,7 and 5% (present study).
In a similar study, Blackwell et al reported that the 50th percentile of latent-phase duration for nulliparas who underwent labor induction and delivered vaginally was 11 hours, and the 90th percentile was 27 hours. In their study, latent-phase duration was calculated as the time from the initiation of cervical ripening until 4 cm of cervical dilation, and this duration was not correlated with adverse outcomes, either maternal or perinatal.9
The strengths of our data are that they were prospectively accrued, reflect practice patterns and outcomes from 14 centers, and were collected by trained and certified research nurses present during labor