Labour Dynamics After Induction in Nulliparous IVF/ICSI and Spontaneous Pregnancies: A Matched Cohort Study

To compare labour dynamics between nulliparous women with IVF/ICSI and spontaneous conception, and to assess the effect of epidural analgesia on the timing and incidence of vaginal birth using time-to-event methods.

Matched retrospective cohort study.

Tertiary referral centre, Bologna, Italy.

A total of 124 IVF/ICSI and 248 maternal age-matched spontaneous conceptions undergoing induction of labour at ≥ 37 weeks between January 2019 and December 2023.

Time-to-vaginal-delivery patterns were evaluated using smoothed instantaneous hazard (SIH) functions. Caesarean delivery was treated as a competing event, and subhazard ratios (sHR) were estimated using Fine-Grey regression. Analyses were stratified by epidural analgesia and adjusted for cervical dilation at induction, body mass index at term, and induction-related variables.

Labour dynamics and cumulative incidence of vaginal delivery over time.

Among 372 inductions, spontaneous conceptions had higher vaginal delivery rates than IVF/ICSI pregnancies (85.1% vs. 72.6%, p = 0.005) and shorter active labour (167 vs. 272 min, p < 0.001). SIH curves showed earlier and more sustained peaks with late-labour rebound in spontaneous conceptions, whereas IVF/ICSI pregnancies exhibited flatter, persistently lower hazards. IVF/ICSI conception was associated with a significantly lower cumulative incidence of vaginal birth (sHR 0.67, p < 0.001). Epidural analgesia delayed the timing but did not reduce the overall likelihood of vaginal delivery in spontaneous conceptions, while no significant effect was observed in IVF/ICSI pregnancies.

Labour dynamics differ by mode of conception. IVF/ICSI pregnancies show reduced labour progression and earlier transition to caesarean delivery.