Advanced labor cesarean birth raises future preterm birth risk

Scarring in the wound linked to increased preterm birth risk in future pregnancies is 8 times more likely in women with cesarean birth at an advanced stage of labor, according to data published in the American Journal of Obstetrics & Gynecology.¹

Increased odds of a low scar were also observed when the baby had a low position. Investigators concluded these findings may be used to improve follow-up care and identify ways to avoid preterm birth in future pregnancies.¹

“Cesarean birth in advanced labor is known to be linked with preterm birth. Our findings highlight the importance of healing of the cesarean scar in the womb and that the stage of labor and low position of the baby can impact how this happens,” said Anna David, PhD, director of the EGA Institute for Women’s Health.¹

Methods of cesarean scar assessment

The observational cohort study was conducted to evaluate factors influencing cesarean scar morphology.² Patients undergoing cesarean delivery (CD) during active labor at 37 weeks’ gestation or later for a singleton pregnancy from January 2021 to October 2022 were included in the analysis.

Exclusion criteria included prior non-CD uterine surgery and multiple CDs. Patients underwent transvaginal ultrasound assessments 4 to 12 months after delivery using the Voluson E8 or E10 Expert US system (GE Healthcare, Austria).²

Parameters for CD scar assessment included depth and width, niche length, residual and adjacent myometrial thickness, and scar distance to the internal cervical os. Anatomical landmarks were used to identify the internal cervical os, with the distance from the CD scar niche measured using calipers.²

Identification of a CD scar and detriments of its location were reported as the primary outcome of the analysis. CD scar healing parameters and scar morphology were reported as secondary outcomes.²

Key CD scar findings

There were 93 participants aged a median 34±4 years and with a median first-trimester body mass index of 23±3 kg/m2 included in the analysis. Delayed labor progress was the primary indication for CD in 43%, pathological intrapartum cardiotocograph trace monitoring in 35.5%, and chorioamnionitis in 11.8%.²

A median cervical dilatation of 9 cm was reported at CD, and advanced labor was reported in 61.3% of cases. A mean 7±2 months occurred between birth and ultrasound evaluation. Of cases:

• 96.8% had a CD scar
• 37.8% had a niche
• And 26.7% had a healing ratio of 0.5 or less.

Of scar locations, 57.8% were cranial, 21.1% at, and 21.1% caudal to the internal cervical os. A 7-fold increase in low fetal station risk was reported for advanced labor CD vs early labor CD, with a relative risk (RR) of 7.3. For cervical scar location at or caudal to the internal os, the RR was 7.8, indicating an 8-fold rise in risk.²

Increased risk associated with advanced labor

After advanced labor, CD scars were 3.7 mm more caudally located in the uterus or cervix vs early labor CD scars. Additionally, significant associations with scar position were reported for cervical dilation and fetal station at CD, with each centimeter increase in cervical dilation positioning the scar 0.88 mm more caudally in the uterus or cervix.²

An area under the curve of 0.819 was reported for cervical dilation vs 0.705 for fetal station toward predicting low CD scar position, highlighting greater predictive power from the former method. Overall, both methods independently predicted cesarean scar location.²

“This new research paves the way for better prediction and prevention of preterm birth following a previous cesarean birth. We’re working closely with health care professionals to make sure this research breakthrough translates to improvements in care,” said Jyotsna Vohra, PhD, MSc, Director of Research, Programmes and Impact at Tommy’s.¹

Ongoing challenges

Despite these outcomes, data discussed by Brittany L. Ranchoff, PhD, MPH, Research Fellow at the Harvard Pilgrim Health Care Institute and Harvard Medical School, has highlighted limited labor after cesarean (LAC) access in certain regions.³ This included LAC access in only 15.9% of US counties during the study period.

“Overall, access is not expanding, at least at the county level,” said Ranchoff.³

References

1. Study highlights risks of Caesarean births to future pregnancies. University College London. October 7, 2025. Accessed October 14, 2025. https://www.eurekalert.org/news-releases/1100999.
2. Ivan M, Banerjee A, Colley C, et al. Postnatal healing of cesarean scar: an ultrasound study. Am J Obstet Gynecol. 2025. doi:10.1016/j.ajog.2025.09.013
3. Ranchoff BL. Brittany Ranchoff, PhD, MPH, highlights limited labor after cesarean access. Contemporary OB/GYN. September 5, 2025. https://www.contemporaryobgyn.net/view/brittany-ranchoff-phd-mph-highlights-limited-labor-after-cesarean-access.