Starting time for induction of labor and the risk for night-time delivery

ObjectiveTo analyze if starting time for labor induction affected the risk of night-time delivery, and to evaluate to what extent the risk was influenced by Bishop score at start of induction, mode of induction, and parity.MethodA retrospective cohort study of women who delivered at Danderyd Hospital, Stockholm, Sweden, 2002–2006, comprising 1940 women induced by Dinoprostone (PGE2) or transcervical balloon catheter (BARD). Risks for night-time delivery were calculated as absolute risk and Odds Ratios by unconditional logistic regression using induction of labor in the morning as reference.ResultsFor nulliparae with Bishop score 0–3 induced by BARD, odds ratios for night-time delivery were 0.42 (95% C.I. 0.19–0.93) and 0.09 (95% C.I. 0.02–0.47) when inductions started in the afternoon and evening, respectively, compared to inductions starting in the morning For multiparae, however, the risk of night-time delivery was highest if induction started in the evening. Compared to inductions started in the morning, odds ratios for night-time delivery were 3.53 (95% C.I. 2.57–4.83) and 8.49 (95% C.I. 4.45–16.19) for induction starting in the afternoon and evening, respectively.ConclusionStarting time of labor induction affects the risk of giving birth at night. For nulliparae induced by BARD, starting the induction in the evening instead of during the day may reduce the number of night-time deliveries substantially. For multiparae, however, our data suggest that induction of labor should take place in the morning.