Impaired healing of cesarean delivery (CD) scars is a critical clinical concern due to the formation of scar niches, which can lead to persistent gynecological symptoms and complications in future pregnancies.¹ Increasing evidence suggests that scar positioning near or within the cervix significantly raises the risk of spontaneous preterm birth.¹ However, the factors influencing scar position and healing remain inadequately understood.¹ A new prospective ultrasound study published in the American Journal of Obstetrics & Gynecology sheds light on this issue, demonstrating that advanced cervical dilation and low fetal station contribute to the formation of scars in cervical locations.¹ These factors are associated with poorer healing outcomes and increased obstetric risks.¹

Global cesarean section rates have surged from 7% in 1990 to 21% today, with projections suggesting they may reach 29% by 2030—exceeding the World Health Organization (WHO)'s recommended 10%-15% threshold.² Impaired healing—identified via ultrasound by the presence of a niche (≥2mm)—is often associated with long-term gynecological issues, fertility impediments, and obstetric complications like uterine rupture in subsequent pregnancies.³ Currently, there is no standard protocol for the management of postnatal cesarean scars, and the variables affecting their development are still being researched.¹

To investigate these issues, researchers conducted a prospective observational study at University College London Hospital, involving 93 women who underwent CD during active labor (4-10cm cervical dilation) between January 2021 and October 2022.¹ Participants underwent standardized transvaginal ultrasound assessments between 4 and 12 months postpartum to evaluate scar characteristics and their alignment relative to the internal cervical os.¹ Impaired healing was defined by the emergence of a niche or a myometrial thickness ratio of ≤0.5.¹

The cohort had a median age of 34 years and a median BMI of 23kg/m².¹ Among participants, cesarean scars were identifiable in 96.8%, with over a third developing a niche.¹ Notably, scars situated at or below the internal os were linked to a higher likelihood of niche formation (relative risk [RR]=1.7; 95% CI: 1.0-3.0; p=0.041) and poorer healing ratios (RR=2.7; 95% CI: 1.3-5.7; p=0.005).¹ Both cervical dilation and fetal station significantly impacted scar position (p<0.001), with advanced labor (8-10cm dilation) resulting in an approximately eightfold greater chance of the scar lying at or below the internal os (RR=7.77; 95% CI: 2.59-23.39; p<0.001).¹ Each additional centimeter of cervical dilation shifted the scar 0.88mm further caudally (95% CI: 0.62–1.14; p<0.001), while each centimeter of fetal descent moved the scar an additional 1.5mm downward (95% CI: 0.71–2.33; p<.001).¹

Maternal characteristics and surgical techniques also appeared to affect healing outcomes.¹ Higher BMI (≥25), maternal age (≥40 years), gestational age (>40 weeks), and increased uterine artery Doppler resistance correlated with impaired healing (all p<0.05).¹ Additionally, the use of locking sutures during closure significantly increased the risk of scar niche formation.¹ Specifically, using a locked first layer followed by an unlocked second layer doubled the risk (RR=2.2; 95% CI: 1.2-4.0; p=0.008), while locking both layers tripled it (RR=3.3; 95% CI: 1.8-6.1; p=0.009), even when adjusted for confounding variables.¹

In conclusion, this study illustrates that the stage of labor at which a cesarean delivery occurs has a profound effect on the placement and healing quality of the uterine scar.¹ Scars located near or within the cervix are particularly susceptible to poor healing.¹ Clinicians are encouraged to counsel women undergoing cesarean delivery in advanced labor about the increased risk of adverse outcomes in subsequent pregnancies and to refer them for monitoring in specialized services aimed at preventing preterm birth.¹