Elective induction of labour and caesarean section in low-moderate risk
nulliparous women: a retrospective cohort study
Abstract
Objective: To evaluate whether elective induction of labour (eIOL)
influences the rate of caesarean birth in uncomplicated pregnant women
at term, compared to expectant management. Design: Retrospective cohort
study. Setting: Births in Victoria between 2010 and 2018. Population:
Term, singleton, vertex births from low-moderate risk pregnancies
(n=396,164). Methods: Preliminary analyses compared eIOL at 37 weeks
with expectant management both beyond that gestational age (preliminary
analysis I) and at that gestational age and beyond (preliminary analysis
II). Similar comparisons were made for eIOL at 38, 39, 40 and 41 weeks’
gestation and expectant management. The primary analysis repeated these
comparisons, limiting the population to nulliparous women whose recorded
indication for induction did not include one of a specified list of
conditions. Chi-square tests and multivariable logistic regression were
used. Adjusted odds ratios and 99% confidence intervals were reported.
P<0.01 denoted statistical significance. Main Outcome
Measures: Unplanned caesarean birth, perinatal mortality Results: The
proportion of nulliparous, low-moderate risk women who underwent IOL ≥37
weeks’ gestation in Victoria increased from 24.6% in 2010 to 30.0% in
2018 (p-value <0.001). eIOL in nulliparous women was
associated with an increased odds of caesarean birth when performed at
38 (aOR 1.23((1.13-1.32)), 39 (aOR 1.31((1.23-1.40)), 40 (aOR
1.42((1.35-1.50)), and 41 weeks’ gestation (aOR 1.43((1.35-1.51)).
Perinatal mortality was rare in both groups and non-significantly lower
in the induced group at most gestations. Conclusions: eIOL was
associated with an increased odds of caesarean birth from 38 weeks’
gestation and a decrease in the odds of perinatal mortality.