The association between induction of labour at 38 to 39 weeks pregnancy and indication for caesarean delivery : an observational study

Background: Induction of labour is associated with a reduction in caesarean delivery, but the mechanism of action and which groups of women might benefit remain unknown. Aims: To assess the association between induction of labour at 38–39 weeks pregnancy, and caesarean delivery: (i) overall; (ii) for slow progress in labour; and (iii) for suspected fetal compromise. Material and methods: Retrospective observational study in two Sydney hospitals from 2009 to 2016, among nulliparous women with induction of labour at 38 or 39 completed weeks pregnancy and a singleton, cephalic presenting fetus. The comparator was all planned vaginal births beyond 39(+1/7) weeks, whether or not labour was induced. Binary and multinomial multiple logistic regressions adjusting for multiple confounders were performed. Results: There were 2388 and 15 259 women in the study and comparison groups respectively. Induction of labour was associated with caesarean delivery overall only for women <25 years of age (adjusted odds ratio 1.63; 95% CI 1.17–2.27) and was not associated with caesarean delivery for slow progress. Induction of labour was positively associated with increased caesarean delivery for suspected fetal compromise among young women (<30 years), with the association weakening as maternal age increased. The association between induction of labour and caesarean delivery was different for slow progress compared with suspected compromise (P = 0.005). Conclusions: Induction of labour has different effects on the likelihood of caesarean delivery for slow progress and for suspected fetal compromise. Women <30 years of age are at higher risk of caesarean delivery for suspected fetal compromise, potentially due to uterine hyperstimulation.