A prospective British ultrasound study has reported an eightfold increase in the risk for cervical scarring in mothers who have cesarean delivery (CD) during advanced labor.

Postnatal ultrasound identified suboptimally healed scars within the cervix after advanced labor CD.

Writing in the American Journal of Obstetrics and Gynecology, Maria Ivan, MD, maternal-fetal medicine trainee at the EGA Institute for Women’s Health at University College London, London, England, and colleagues noted that impaired healing of cesarean scars can result in long-term complications because of the formation of a scar niche. Also known as an isthmocele, the niche is a pouch-like indentation in the uterine myometrium at the site of a CD incision that does not heal completely. In these pouch-like areas, blood can accumulate and may lead to postmenstrual spotting, dysmenorrhea, and chronic pelvic pain. Isthmocele can impair fertility and adversely affect future pregnancies.

“Moreover, there is increasing evidence that a cesarean delivery scar located close to or within the cervix is associated with an increased risk of subsequent spontaneous preterm birth,” the University College London authors wrote.

Ivan noted that 42% of UK births now occur by CD, with the future risk for preterm birth highest when a previous CD was performed at full dilatation.

There has been a knowledge gap regarding the underlying mechanisms driving this association. The study was designed to address this gap by examining postnatal scar location and healing following labor, she told Medscape Medical News.

Study Details

This observational study is the first to look at the site of damage in the uterus and cervix in relation to how advanced the labor is at CD.

The investigators recruited a cohort of 93 women, mean age 34 years, undergoing cesarean section during active labor at cervical dilatation of 4-10 cm in a University College London hospital from January 2021 to October 2022.

Transvaginal ultrasound 4-12 months postpartum evaluated scar characteristics and location relative to the internal cervical os.

Scars were identified in 90 of the 93 (96.8%) women. In 52 mothers (57.8%), scars were situated higher in the womb, while those in the rest were located either close to the cervix (19 women, 21.1%) or within it (also 19 women, 21.1%).

Indicators of impaired scar healing were the presence of a scar niche with a depth of ≥ 2 mm and/or a healing ratio ≤ 0.5. The ratio is an ultrasonic comparison of the thickness of the thinned myometrium at the scar site to the thickness of the adjacent healthy myometrium or cervix and is considered an indicator of healing.

While the results were consistent with the hypothesis that full dilatation leads to more caudally positioned scars, Ivan said, “What was unexpected was the degree of this effect. Even women who had a cesarean at 8 or 9 cm dilatation frequently demonstrated scars extending to or below the internal cervical os.”

In specific findings:

• Advanced labor CD (8-10 cm dilatation) was associated with an eightfold increased likelihood of a scar located at or caudally (lower) to the internal os (relative risk [RR], 7.77; 95% CI, 2.59-23.39; P < .001) vs cesarean birth performed earlier in labor (4-7 cm dilatation).
• Cervical dilatation and fetal station at surgery significantly influenced scar position relative to the internal cervical os (P < .001). Low-lying scars did not heal as well as those higher up.
• Niche prevalence was 37.8% (34 of 90), of which 67.6% (23 of 24) had a poor healing ratio of ≤ 0.5.
• Risk factors for suboptimal scar healing included a BMI ≥ 25, increased uterine artery vascular Doppler resistance, and gestational age > 40 weeks. Other risk factors were the use of locking sutures during surgery and scar location caudal to the internal os on postnatal ultrasound (P < .05).

“Women who undergo cesarean birth in advanced labor should be counseled regarding the increased risk of adverse outcomes in subsequent pregnancies and should be referred for surveillance in a dedicated preterm birth prevention service,” Ivan advised.

“For those who develop symptoms that can be attributed to a scar niche — such as postmenstrual bleeding, pelvic pain, or secondary subfertility — early gynecologic referral is recommended.” More data are required to evaluate the impact of surgical correction on both symptom control and reproductive outcomes in this population.

Offering a US perspective on the study, Vincenzo Berghella, MD, a professor of ob/gyn and director of the Division of Maternal and Fetal Medicine at Jefferson Health, Thomas Jefferson University in Philadelphia, called the study timely in light of the increasing global trend toward cesarean deliveries. “These account for more than 21% of deliveries annually in the world and 32% in the United States,” he said.

He suggests doing the uterine incision for CD higher on the uterus, especially if the cervix is > 8 cm dilated, to avoid putting the scar in the cervix. As the UK study suggests, doing an ultrasound 6 months after CD can identify a niche, he said. “But I think the future of management will be to do the first CD, and every CD, with the right identified technique for preventing any future niche.”

Ivan’s message to women is a positive one. “For mothers, it’s important to understand that cesarean birth remains a safe and essential intervention for both mother and baby. However, awareness of the associated risks, informed counseling, and shared decision-making are key components of modern obstetric practice.”