Determinants of First-Trimester Residual Myometrial Thickness After Previous Cesarean Delivery: A Retrospective Cohort Study.

Background and

Objectives

To investigate factors associated with first-trimester residual myometrial thickness (RMT) at the site of a previous cesarean section scar and to evaluate the relationship between RMT and selected pregnancy and neonatal outcomes. Materials and

Methods

This retrospective cohort study included 80 pregnant women with at least one previous CS who attended the Department of Obstetrics and Gynecology, Uludağ University Faculty of Medicine, between July 2017 and December 2018. RMT at the cesarean scar site was measured by transvaginal ultrasonography (TVUS) during the first trimester. After exclusion of 15 women because of incomplete records or missing follow-up data, 65 patients were included in the final analysis. Participants were categorized according to first-trimester RMT as a thin scar group (RMT ≤ 8 mm, n = 37) and a control group (RMT > 8 mm, n = 28). Demographic characteristics, obstetric history, cesarean-related variables, postpartum hemorrhage (PPH) history, ultrasonographic findings, and neonatal outcomes were analyzed. Statistical analyses included Student's t-test, chi-square test, one-way analysis of variance (ANOVA), and Spearman correlation analysis.

Results

Women with thinner residual myometrium had significantly higher parity (p = 0.003), a greater number of previous cesarean deliveries (p = 0.016), and a higher frequency of previous PPH (p = 0.037) compared with controls. Mean RMT was significantly lower in women with parity ≥ 2 than in women with parity 1 (6.39 ± 2.76 mm vs. 8.51 ± 2.81 mm, p = 0.003). Similarly, women with a history of PPH demonstrated significantly lower RMT than those without such a history (5.67 ± 2.11 mm vs. 7.82 ± 2.98 mm, p = 0.037). Correlation analysis revealed a moderate inverse relationship between the number of previous cesarean deliveries and RMT (r = -0.463, p < 0.001). No significant group differences were observed regarding cervical length, placental location, gestational age at delivery, 5 min Apgar score, or birth weight.

Conclusions

First-trimester RMT was significantly associated with parity, previous cesarean delivery number, and a history of PPH. Among the evaluated variables, the number of previous cesarean deliveries demonstrated the strongest independent association with reduced RMT. These findings suggest that early transvaginal ultrasonographic assessment of RMT may serve as a useful sonographic marker of cesarean scar morphology and healing characteristics in pregnancies following cesarean delivery. Larger prospective studies are needed to determine the clinical significance of first-trimester RMT measurements for subsequent obstetric outcomes.