Outcomes of induction of labour in nulliparous women at 38 to 39 weeks pregnancy by clinical indication : an observational study

Background: Knowledge of the outcomes of induction of labour for different indications is sparse. Aims: To describe the mode of birth and other outcomes for nulliparous women induced at 38–39 weeks gestational age by indication for induction of labour. Material and methods: This was a retrospective observational study in a tertiary referral hospital, and a metropolitan teaching hospital in Sydney. The study population was nulliparous women with induction of labour at 38 or 39 completed weeks of pregnancy and a singleton, cephalic presenting baby planning a vaginal birth, from 2009 to 2016. The indication for induction of labour was classified into 12 groups. Mode of birth and other maternal and perinatal outcomes were described in each group, for women who spontaneously laboured at 38 or 39 weeks, and for women who gave birth from 40 completed weeks onward. The main outcome measure was mode of birth. Results: There were 3330 women with induction of labour at 38 or 39 weeks gestation. Rates of vaginal birth varied widely, ranging from 54% when the indication for induction was suspected large fetus, to 82% when the indication was suspected fetal compromise, and was 74% overall. Indications for caesarean delivery also varied by indication for induction. Among women giving birth ≥40 weeks gestational age, 75% had a vaginal birth. Conclusions: In nulliparous women, rates of vaginal birth following induction of labour at 38 or 39 weeks gestation vary widely according to the indication for induction. These data are useful for antenatal counselling.