Postnatal healing of cesarean scar: an ultrasound study

Impaired healing of cesarean delivery scars results in long-term complications, including scar niche formation, which may adversely impact future pregnancies and lead to gynecological symptoms such as postmenstrual spotting, dysmenorrhea, and chronic pelvic pain. 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 factors influencing cesarean birth scar location and healing remain poorly understood.

We explored the impact of antenatal, intrapartum, intraoperative, and postnatal factors on cesarean scar sonographic healing, location, and morphology after cesarean delivery in labor.

This prospective observational cohort study recruited women who underwent cesarean delivery during active labor (cervical dilation 4-10 cm) at the University College London Hospital, UK (January 2021-October 2022). Transvaginal ultrasound was performed 4 to 12 months postpartum to evaluate cesarean delivery scar characteristics and location relative to the internal cervical os. Indicators of impaired scar healing were presence of a scar niche (depth ≥2 mm) and/or a healing ratio (residual/adjacent myometrial or cervical thickness) of ≤0.5. Regression analysis assessed the associations between clinical variables and cesarean scar parameters.

Cesarean delivery scars were identified in 96.8% of women recruited (90/93). Advanced labor cesarean delivery (8-10 cm dilatation) was associated with an 8-fold increased likelihood of a scar located at or caudal to the internal os (relative risk, 7.77; 95% confidence interval, 2.59, 23.39; P<.001) compared to 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). For each 1 cm increase in cervical dilatation during labor, the scar was positioned 0.88 mm more caudally on the uterus or cervix (95% confidence interval, 0.62, 1.14; P<.001). Similarly, for each 1 cm descent of the fetal part within the maternal pelvis, the cesarean scar was located 1.5 mm more caudally on the uterus or cervix (95% confidence interval, 0.71, 2.33; P<.001). The niche prevalence was 37.8% (34/90), of which 67.6% (23/34) had a healing ratio ≤0.5. Risk factors for suboptimal scar healing included body mass index ≥25, increased uterine artery vascular Doppler resistance, gestational age >40 weeks, the use of locking sutures during surgery, and cesarean delivery scar location caudal to the internal os on postnatal ultrasound (P<.05). Uterine scars, situated cranial to the internal os, had significantly larger niche dimensions compared to those located within the cervix, at or caudal to the internal os (P<.05).

Advanced cervical dilatation and low fetal station at emergency cesarean delivery in labor are independent predictors of cesarean scar location near or within the cervix, and these cervical scars heal less well than scars located higher in the uterus. Even women having a cesarean birth at 8 to 9 cm have a high risk of the scar being close or within the cervix, which is known to increase the risk of subsequent spontaneous preterm birth. Further research is needed into the impact of cesarean scar characteristics on gynecologic symptoms and future pregnancy outcomes and to develop techniques to improve cesarean scar healing.