Prolonged Second Stage of Labor in Thai Women: A Retrospective Cohort Study.

Objective: To assess the natural course of the second stage of labor in Thai women. Methods: A retrospective cohort study was conducted on singleton pregnancies during the second stage of labor, which were categorized into prolonged and non-prolonged groups using group-specific 95th-percentile cut-offs for nulliparous and multiparous women. The natural course of the second stage was evaluated, and adverse delivery outcomes were compared between the two groups. Results: When the 95th percentile was used to define prolonged second stages, durations of 80 and 58 minutes were the appropriate cut-offs for nulliparous and multiparous women, respectively, substantially shorter than those reported in other ethnic groups. Overall cesarean section rate (CSR) was very low (1.4%), with most of them performed in the prolonged group. After adjusting for confounders, a prolonged second stage was an independent risk of CSR (odds ratio: 175 and 221 for nulliparous and multiparous, respectively), operative vaginal delivery, low Apgar scores, and postpartum hemorrhage in both nulliparous and multiparous women. Cesarean deliveries were performed significantly earlier among multiparas but the CSR was comparable. Conclusion: The second stage of labor in Thai women is markedly shorter than that reported in Western populations. The definition of a prolonged second stage should be tailored to specific ethnic populations, and the current ACOG/SMFM criteria may not be appropriate for Thai women. Among the Thai population, cut-off values of 80 minutes for nulliparous women and 60 minutes for multiparous women may be appropriate for defining a prolonged second stage. A prolonged second stage markedly increased the rates of cesarean section rate, operative vaginal delivery, low Apgar scores and postpartum hemorrhage. However, the overall cesarean rate during the second stage remained very low in Thai women.