Labour Progression Differences Between IVF/ICSI and Spontaneous Pregnancies Following Induction: Insights from a Matched Cohort Study

Highlight

• Labour progression post-induction is significantly slower in nulliparous IVF/ICSI pregnancies than in spontaneous conceptions.
• IVF/ICSI pregnancies show reduced cumulative incidence of vaginal delivery and earlier transition to cesarean section.
• Epidural analgesia delays labour timing in spontaneous conceptions without reducing vaginal birth rates but has no significant effect on IVF/ICSI pregnancies.
• Time-to-event analysis with competing risk modeling provides nuanced insight into labour dynamics by conception mode.

Study Background

Assisted reproductive technologies such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) have led to increased pregnancies worldwide. However, pregnancies conceived through these methods may carry distinct obstetric risks compared to spontaneous conceptions. One such area of interest is labour dynamics, particularly following induction at term, which is common in clinical practice for various maternal or fetal indications. Understanding if and how labour progression differs after induction in IVF/ICSI versus spontaneous pregnancies is crucial for optimizing labour management and counseling.

Previous data have suggested altered placental function, uterine contractility, and cervical remodeling in IVF/ICSI pregnancies, which could influence labour. Yet, robust, comparative analyses accounting for confounding factors like maternal age, body mass index (BMI), and epidural analgesia are limited. This knowledge gap motivates the present matched cohort study conducted at a tertiary referral center in Bologna, Italy, investigating the labour course after induction in nulliparous women.

Study Design

This study employed a retrospective matched cohort design including 124 nulliparous women who conceived via IVF/ICSI and underwent labour induction at or beyond 37 weeks gestation. They were matched 1:2 by maternal age to 248 spontaneous conception nulliparas also undergoing induction between 2019 and 2023. Matching on age helped control for a key confounder affecting labour outcomes.

Labour induction protocols, cervical dilation at induction, BMI at term, and use of epidural analgesia were recorded. The primary analytic approach involved time-to-event methods: smoothed instantaneous hazard (SIH) functions modeled the hazard of vaginal delivery over time, while cesarean delivery was treated as a competing risk analyzed via Fine-Gray regression estimating subhazard ratios (sHR). Analyses further stratified by epidural analgesia use and adjusted for relevant variables.

Key Findings

Among the 372 inductions analyzed, women with spontaneous conceptions had significantly higher vaginal delivery rates (85.1%) compared to those with IVF/ICSI pregnancies (72.6%), with a p-value of 0.005. Active labour duration was notably shorter in spontaneous conceptions, median 167 minutes versus 272 minutes in IVF/ICSI cases (p < 0.001).

The SIH curves revealed distinct labour progression patterns: spontaneous conception women experienced earlier, sharper peaks in hazard of vaginal delivery with a characteristic late-labour hazard rebound. Conversely, IVF/ICSI pregnancies exhibited a flatter hazard curve, with consistently lower hazards over time, indicating slower progression.

The Fine-Gray competing risk model showed that IVF/ICSI conception was independently associated with a 33% reduction in the cumulative incidence of vaginal delivery (subhazard ratio 0.67, p < 0.001), adjusting for cervical dilation, BMI, and induction-related factors.

Epidural analgesia delayed the timing of vaginal delivery in spontaneous conception pregnancies but did not diminish the overall likelihood of vaginal birth. In IVF/ICSI pregnancies, epidural use did not have a statistically significant impact on timing or incidence of vaginal delivery.

Expert Commentary

This study provides an important contribution to labour management in pregnancies conceived via ART. The slower labour progression and reduced vaginal delivery incidence suggest possible physiological differences in the uterine or cervical response to induction in IVF/ICSI pregnancies. Potential explanations include altered myometrial contractility or cervical remodeling associated with ART conception or underlying infertility factors.

The use of robust time-to-event competing risk methodology strengthens the validity of findings, overcoming limitations of traditional labour duration comparisons. Stratification by epidural analgesia use and adjustment for confounders enhances clinical applicability.

Study limitations include its retrospective design and lack of detailed mechanistic data such as uterine contractility patterns or biochemical markers. Also, as a single-center study, results may not fully generalize to other populations or induction protocols.

Future research should investigate biological mechanisms underpinning these differences and explore tailored induction protocols or labour management strategies to optimize outcomes in IVF/ICSI pregnancies.

Conclusion

Labour dynamics following induction differ significantly between nulliparous IVF/ICSI and spontaneous pregnancies. IVF/ICSI pregnancies demonstrate slower active labour progression and a lower cumulative incidence of vaginal delivery, with a tendency toward earlier transition to cesarean delivery. Epidural analgesia delays labour timing in spontaneous conceptions but does not reduce vaginal birth rates, with no significant effect observed in IVF/ICSI pregnancies.

Recognition of these differences can aid clinicians in counseling, planning labour induction strategies, and setting realistic expectations. Tailored clinical protocols may be warranted to improve labour outcomes in this growing patient population.

Funding and Clinicaltrials.gov

Information on funding sources and clinical trial registration was not provided in the original publication.

References

Seidenari A, Doroldi S, Rinaldi MC, Calisti S, Sollevanti C, Scollo C, Scibilia G, Morano D, Farina A. Labour Dynamics After Induction in Nulliparous IVF/ICSI and Spontaneous Pregnancies: A Matched Cohort Study. BJOG: An International Journal of Obstetrics and Gynaecology. 2026 Jul 6. PMID: 42410324.

American College of Obstetricians and Gynecologists. Induction of Labor. Practice Bulletin No. 107. Obstet Gynecol. 2009;114(2 Pt 1):386-397.

Galbally M, Watson CJ, Lowen G. Physiology and Pathophysiology of Uterine Contractility. Semin Fetal Neonatal Med. 2020;25(6):101156.