Introduction: Birth at early term (37(+0) -38(+6) completed gestational weeks [GW] and additional days) is associated with adverse neonatal outcomes compared with waiting to >= 39 GW. Most studies report outcomes after elective cesarean section or a mix of all modes of births; it is unclear whether these adverse outcomes apply to early-term babies born after induction of labor (IOL). We aimed to determine, in women with a non-urgent induction indication (elective/planned >48 h in advance), if IOL at early and late term was associated with adverse neonatal and maternal outcomes compared with IOL at full term.

Material and methods: An observational cohort study as a secondary analysis of a multicenter randomized controlled trial of 1087 New Zealand women with a planned IOL >= 37(+0) GW. Multivariable logistic regression was used to analyze neonatal and maternal outcomes in relation to gestational age; 37(+0) -38(+6) (early term), 39(+0) -40(+6) (full term) and >= 41(+0) (late term) GW. Neonatal outcome analyses were adjusted for sex, birthweight, mode of birth and induction indication, and maternal outcome analyses for parity, age, body mass index and induction method. The primary neonatal outcome was admission to neonatal intensive care unit (NICU) for >4 hours; the primary maternal outcome was cesarean section.

Results: Among the 1087 participants, 266 had IOL at early term, 480 at full term, and 341 at late term. Babies born following IOL at early term had increased odds for NICU admission for >4 hours (adjusted odds ratio [aOR] 2.16, 95% confidence intervals (CI) 1.16-4.05), compared with full term. Women having IOL at early term had no difference in emergency cesarean rates but had an increased need for a second induction method (aOR 1.70, 95% CI 1.15-2.51) and spent 4 h longer from start of IOL to birth (Hodges-Lehmann estimator 4.10, 95% CI 1.33-6.95) compared with those with IOL at full term.

Conclusions: IOL for a non-urgent indication at early term was associated with adverse neonatal and maternal outcomes and no benefits compared with IOL at full term. These findings support international guidelines to avoid IOL before 39 GW unless there is an evidence-based indication for earlier planned birth and will help inform women and clinicians in their decision-making about timing of IOL.