Duration of the second stage of labour and risk of subsequent spontaneous preterm birth

Objectives: To determine the risk of spontaneous preterm birth (sPTB) associated with the length of second stage of labour in the first term delivery. Design: Retrospective cohort study. Setting: University hospital. Population: Women with first two consecutive singleton births and the first birth at term. Those who did not reach the second stage of labour in the first delivery were excluded. Methods: Charts from 2007 to 2019 were reviewed. Main outcome measures: Rate of sPTB (<37 weeks of gestation) in the second delivery. Results: Of 13 958 women who met study inclusion criteria, 1464 (10.5%) parturients had a prolonged second stage (≥180 min) in their first term delivery. The rate of sPTB in the second delivery was similar in those with and without a prolonged second stage in first delivery (2.8% versus 2.8%; adjusted odds ratio [aOR] 1.35, 95% CI 0.96–1.90). After adjustment for mode of delivery, prolonged second stage was also not associated with subsequent sPTB in those who delivered by spontaneous and operative vaginal delivery. Those delivered by second-stage caesarean section in the first delivery had a higher risk of sPTB in the second delivery (25/526, 4.8%; aOR 2.66, 95% CI 1.71–4.12; p < 0.001), with a more pronounced risk in those with second-stage caesarean following a prolonged second stage of labour (15/259, 5.8%; aOR 3.40, 95% CI 1.94–5.94; p < 0.001). Conclusion: Second-stage duration in a first term vaginal delivery is not associated with subsequent sPTB. The risk of sPTB is increased following second-stage caesarean section, particularly if performed after a prolonged second stage. Tweetable abstract: Second-stage caesarean delivery, particularly after prolonged second stage, increases the risk of preterm birth.