When a baby is born by C-section, recovery usually focuses on the visible scar, the one on the abdomen. But new research shows the scar is gone within the uterus can tell a more complicated story, especially when the caesarean section takes place in the later stages of labor.
Researchers from University College London (UCL) found that women who have a caesarean section at an advanced stage of labor – when the cervix is ​​almost or fully dilated – are eight times more likely to develop scars lower in the uterus, near or even in the cervix. These scars tend to heal less effectively and are associated with a greater chance of complications in future pregnancies, including preterm birth.
The research, published in American Journal of Obstetrics & Gynecologylooked at how the stage of labor when a caesarean section is performed affects where the internal scar forms and how well it heals.
The team studied 93 women who had a cesarean delivery during active labor, defined as the cervix being at least four centimeters dilated. Each participant underwent a detailed transvaginal ultrasound between four and twelve months postpartum to assess the location and condition of the scar.
Of these, almost all (90 out of 93) were found to have a visible internal scar.
- 52 women (57.8%) had marks higher up on the uterus.
- 19 women (21.1%) she had scars near her cervix.
- 19 women (21.1%) he had scars inside the cervix itself.
The researchers found a clear pattern:
- For every additional centimeter of cervical dilation during labor, the scar formed 0.88 mm lower in the uterus.
- Women who had a C-section when their cervix was almost or completely dilated (about 8-10 cm) were eight times more likely to have a scar near or inside the cervix compared to those whose surgeries were done earlier in labor.
- A low fetal position – when the baby had already descended deep into the pelvis – also increased the chance of a low scar.
As labor progresses, the cervix softens and opens to allow the baby to pass. In advanced stages of labor, this means that the lower part of the uterus and cervix are more stretched and thinner. When a C-section is performed at this stage, the surgeon often needs to make the incision lower, sometimes extending into the cervix itself.
These low marks don’t always heal well. The study found signs of impaired healing, such as scar “niches,” small pockets or indentations of at least two millimeters in the uterine wall. These sinuses can trap blood after menstruation, leading to spotting, discomfort, and in some cases, infertility or complications during subsequent pregnancies.
The researchers found that scars in or near the cervix were less likely to heal completely than those higher up in the uterus. Women with these low scars were more likely to have thin residual tissue and visible defects on ultrasound, both indicators of poor scar healing.
Dr Maria Ivan, lead author of the study from the EGA Institute for Women’s Health, explained that her team wanted to understand how caesarean section affects the uterus depending on the stage of labour:
“We’ve known that cesarean birth can damage the cervix. Our study is the first to look at where this damage occurs in the uterus, depending on how far along labor is when the procedure is performed. Our findings have important implications for women who have cesarean late in their labor and want to have more children.”
She added that the results may help doctors manage postpartum recovery and future pregnancy care:
“These new insights can help shape future care for women who have cesarean deliveries, helping doctors better prepare women for childbirth, and hopefully also lead to improved surgical techniques that reduce the risk of future complications that cesarean scars can cause.”
In high-income countries, cesarean deliveries are becoming more common. In England, more than 40% of all births are now by caesarean section, up from around 26% a decade ago. In 2023–24, 42% of births were by caesarean section, around 226,000 births, with almost 126,000 of these taking place in emergency situations.
With such a sharp increase, researchers say understanding how and where uterine scars form is more important than ever.
Professor Anna David, co-author and Director at UCL’s EGA Institute for Women’s Health and Associate Director at Tommy’s National Preterm Birth Research Centre, explained:
“Caesarean delivery in advanced labor is known to be associated with preterm birth. Our findings highlight the importance of healing of the caesarean scar in utero and that the stage of labor and the low position of the baby can influence how this happens.”
Dr Jyotsna Vohra, Director of Research, Programs and Impact at the charity Tommy’s, noted that these findings could help reduce anxiety for women who have had emergency caesareans and fear complications in future pregnancies:
“Unplanned cesarean births can be very stressful, especially when they are done in an emergency to make sure the baby arrives safely. Women who have experienced one may already feel anxious about their next pregnancy. This research paves the way for better prediction and prevention of preterm birth after a previous cesarean.”
The team hopes the results will lead to improved postpartum follow-up, early ultrasound follow-up, and surgical improvements that support better healing. They are also calling for more studies to investigate how C-section scars contribute to gynecological symptoms such as pain and bleeding, as well as how they affect fertility.
What parents need to know
- Time matters. C-section deliveries that take place late in labor – when the cervix is ​​almost open – are more likely to result in low-lying scars that heal poorly.
- Ask questions. If you had an emergency or late-stage C-section, ask your provider about where your C-section was performed and whether ultrasound monitoring is recommended.
- Know the signs. Spotting between periods, pain or fertility problems could be linked to a poorly healed uterine scar.
- Follow up care helps. A transvaginal ultrasound four to twelve months after delivery can assess how the scar has healed and guide care for future pregnancies.
C-sections are life-saving procedures, but how and when they are performed can have lasting effects. This new research offers a deeper understanding of what happens inside the uterus after surgery and opens the door to better healing, safer pregnancies and more informed postpartum care.
As Dr. Ivan, “Our goal is to ensure that women who need a C-section today can look forward to safe, healthy pregnancies in the future.”
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