The impact of stage of labor on adverse maternal and neonatal outcomes in multiparous women: a retrospective cohort study

Background The correlation between stage of labor and adverse delivery outcomes has been widely studied. Most of studies focused on nulliparous women, it was not very clear what impact the stage of labor duration had on multiparous women. Methods A retrospective cohort study was conducted among all the multiparous women of cephalic, term, singleton births, who planned vaginal delivery. The total stage of labor covered the first stage and the second stage in this study, and they were divided into subgroups. Adverse maternal outcomes were defined as referral cesarean delivery, instrumental delivery, postpartum hemorrhage, perineal laceration (III and IV degree), hospitalization stay ≥90th, and adverse neonatal outcomes as NICU, shoulder dystocia, Apgar score ≤ 7(5 min), neonatal resuscitation, assisted ventilation required immediately after delivery. Results There were 7109 parturients included in this study. The duration of first stage was 6.2(3.6–10.0) hours, the second stage was 0.3(0.2–0.7) hour, the total stage was 6.9(4.1–10.7) hours in multiparous women. At the first stage, the rates of overall adverse outcome were 21, 23.4, 28.8, 35.5, 38.4% in subgroups < 6 h, 6–11.9 h, 12–17.9 h, 18–23.9 h, ≥24 h, which increased significantly ( X 2 = 57.64, P < 0.001), and ARR (95% CI) were 1.10 (0.92,1.31), 1.33 (1.04,1.70), 1.80 (1.21,2.68), 2.57 (1.60,4.15) compared with subgroup < 6 h (ARR = 1); At the second stage, the rates of overall adverse outcome were 20.0, 30.7, 38.5, 61.2, 69.6% in subgroups < 1 h, 1–1.9 h, 2–2.9 h, 3–3.9 h, ≥4 h ( X 2 = 349.70 , P < 0.001), and ARR (95% CI) were 1.89 (1.50, 2.39), 2.22 (1.55, 3.18), 10.64 (6.09, 18.59), 11.75 (6.55, 21.08) compared with subgroup < 1 h (ARR = 1)). At the total stage, the rates of overall adverse outcome were 21.5, 30.8, 42.4% in subgroups < 12 h, 12–23.9 h, ≥24 h ( X 2 = 84.90 , P < 0.001), and ARR (95% CI) were 1.41 (1.16,1.72), 3.17 (2.10,4.80) compared with subgroup < 12 h (ARR = 1). Conclusions The prolonged stage of labor may lead to increased adverse outcomes in multiparous women, it was an independent risk factor of adverse maternal and neonatal outcomes.