Estimating the probability of spontaneous delivery conditional on time spent in the second stage.

The duration of second stage labour was studied, retrospectively, among 410 primigravidas who received epidural analgesia in the first stage of spontaneous labour at term (greater than 37 weeks). Survival analysis was used to investigate how the likelihood of a spontaneous delivery was related to time spent in the second stage, and how some maternal and fetal factors influenced this relationship. The proportion of spontaneous deliveries that had occurred by any given time was greatly influenced by maternal age and infant birthweight. However, the women who were least likely to have been delivered by any given time after full dilatation, were also the ones who were least likely to be delivered within any given subsequent time interval. If delivery had not occurred by 3 h, the probability that it would take place in the next 3 h was well under 30% in most cases. We conclude that second stage labour in excess of 3 h is likely to be beneficial only if certain criteria, which are defined in the paper, are met.