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Liberalisation of elective induction of labour at 39 weeks in low-risk pregnancies: a retrospective cohort study
Vera Correia1, Sofia Bessa Monteiro2, Marina Moucho2
1Department of Obstetrics and Gynaecology, Médio Ave Hospital Centre, Famalicão, Portugal; Faculty of Medicine of Oporto's University, Oporto, Portugal.
Background:
Since the publication of the ARRIVE trial, elective induction of labour (eIOL) at 39 weeks in low-risk pregnancies has been progressively adopted in clinical practice.
Objectives:
Evaluate the maternal and neonatal outcomes associated with the adoption of a liberal eIOL policy in a Portuguese tertiary centre.
Methods:
Retrospective cohort study conducted at ULS São João, Oporto, of singleton low-risk pregnancies delivered after 39 weeks between two periods: pre-eIOL (2017-2019) and post-eIOL (2022-2024), excluding the pandemic years. Patients with prior or planned caesarean delivery and premature rupture of membranes were excluded. The primary outcome was caesarean delivery rate. Secondary outcomes included maternal and neonatal morbidity. Multivariable logistic regression models adjusted for potentially confounding factors were created.
Results:
Following eIOL policy liberalisation, among 4,893 women (2,602 pre-eIOL; 2,291 post-eIOL), including both nulliparous (n = 2,912) and multiparous (n = 1,981) women, induction rates increased from 22.1% to 43.1% (p < 0.01), with 39-week inductions rising from 4.4% to 16.1% (p < 0.01). Caesarean delivery rates were not significantly different after adjustment (14.1% pre-eIOL to 17.2% post-eIOL, aOR 1.13, 95% CI 0.95-1.34, p = 0.17), while operative vaginal deliveries decreased (30.9% to 26.2%, aOR 0.79, 95% CI 0.69-0.90, p < 0.01) and eutocic vaginal births increased (54.9% to 56.5%, aOR 1.17, 95% CI 1.02-1.33, p = 0.03). Maternal morbidity rose, namely antibiotic use for suspected chorioamnionitis (aOR 1.80, 95% CI 1.25-2.60, p < 0.01), postpartum haemorrhage (aOR 1.86, 95% CI 1.17-2.94, p = 0.01), and longer admission-to-delivery intervals (11.83 to 15.75 h, p < 0.01). Complications arising beyond 39 weeks of gestation declined (aOR 0.66, 95% CI 0.44-0.99, p = 0.04). Most neonatal outcomes remained unchanged. Subgroup and sensitivity analyses were consistent with the primary analysis.
Conclusion:
Liberalisation of elective induction at 39 weeks was associated with a favourable shift in vaginal delivery outcomes without an increase in caesarean delivery rates. However, higher rates of antibiotic use for suspected chorioamnionitis and postpartum haemorrhage were observed.
