New evidence links advanced-labor cesareans to higher womb scar risk
Researchers from University College London (UCL) have identified a strong association between cesarean births performed at an advanced stage of labor and the development of scars inside the uterus that are closer to the cervix. The study, published in the American Journal of Obstetrics & Gynecology, suggests these cervix-adjacent scars may increase the likelihood of premature births in future pregnancies.
In high-income countries, including England, cesarean deliveries now account for more than 40% of births. As labor progresses, the baby moves toward the birth canal and the cervix dilates to up to 10 centimeters in preparation for delivery. When a cesarean is performed for safety reasons, it leaves a scar in the womb. The new findings add a crucial layer to our understanding of where that scar forms and how well it heals, depending on how far labor has progressed.
What the study did
The UCL team followed 93 women who had cesarean births during active labor, defined as the cervix being at least four centimeters dilated. Four to twelve months after birth, transvaginal ultrasounds were used to locate any internal scarring and assess healing. The goal was to see whether the stage of labor at the time of cesarean influenced scar position and healing outcomes.
The results were striking: almost all participants (90 of 93) had a visible internal scar. Importantly, for each additional centimeter of cervical dilation during labor, the scar shifted about 0.88 millimeters lower in the womb and closer to the cervix. This meant that cesareans performed later in labor were far more likely to produce scar tissue near or within the cervix compared with cesareans carried out earlier in labor.
Scar position and healing
About 58% of scars were in the higher part of the uterus, while roughly 21% were near the cervix or inside it. The researchers concluded that advanced-labor cesareans carried an eightfold higher risk of producing a cervix-adjacent scar than cesareans performed earlier in labor.
Healing patterns followed a similar trend. Scar niches, defined as defects in the uterine wall at least two millimeters deep, were more common when scars formed near the cervix. These niches can harbor blood and potentially contribute to infertility, irregular menstruation, or complications in future pregnancies, indicating a greater risk of adverse outcomes down the line.
Implications for care and future research
Lead author Dr. Maria Ivan emphasizes that while cesarean birth is sometimes essential for safety, the location of the scar and how well it heals can have lasting consequences. The study’s findings could inform improved follow-up care for women who undergo cesareans late in labor and guide strategies to reduce the risk of preterm birth in future pregnancies.
Co-author Professor Anna David notes that the stage of labor and the baby’s position at birth influence scar healing, underlining the need for refinements in surgical techniques. The research team advocates for continued investigation into cesarean scar healing and its gynecologic symptoms to better predict and prevent preterm births after a cesarean.
Campaigners from Tommy’s and other health organizations stress that the rise in cesarean births over the past decade means more women will face decisions about subsequent pregnancies. The researchers hope that these insights will translate into practical guidance for clinicians and expectant families, reducing anxiety and improving outcomes for babies at risk of being born too soon.
Context and numbers
England has seen a notable rise in cesarean births, reaching around 42% of all deliveries in 2023/24. The shift underscores the importance of understanding long-term effects, such as uterine scarring, on future pregnancies and maternal health.
