OC136: Factors influencing the lower uterine segment thickness in late pregnancies with previous Cesarean Section

Abstract

Objectives: Several studies have shown that sonographic evaluation of the lower uterine segment (LUS) thickness can predict uterine rupture using either the full LUS thickness or the muscular layer measurement. We aimed to evaluate the potential factors associated with LUS thickness. Methods: A prospective cohort study of women with prior cesarean was conducted. Measurements of the LUS thickness were performed transabdominally and repeated transvaginally if unsatisfactory visualised. The thinnest measurement was considered as the dependant variable. Non-parametric analyses were used to evaluate potential factors associated with LUS thickness including: maternal age, gestational age, interdelivery interval, prior vaginal delivery, and characteristics of the prior cesarean section. Multivariate linear regressions were performed to adjust for confounding variables. Results: 252 women were recruited at a mean gestational age of 36.7 ± 1.3 weeks. In univariate analyses, the only significant factor associated with full LUS thickness was the indication of the prior cesarean (recurrent vs. non recurrent: 3.0 InterQuartile (IQ): 2.4–3.8 mm and 2.5 IQ: 2.0–3.2 mm respectively, P < 0.001). For the muscular layer thickness, the indication (recurrent vs. non recurrent: 1.5 IQ: 1.1–2.1 mm and 1.2 IQ: 0.8–1.8 mm respectively, P < 0.001) and the number of closure layers of the previous cesarean (single vs. double layer : 1.1 IQ: 0.8–1.5 mm and 1.4 IQ: 1.0–1.9 mm respectively, P = 0.02) were significant. The indication of the prior cesarean remained the only significant factor in the linear regression model (P = 0.03). Conclusions: We demonstrated an association between non recurrent indications of prior cesarean and thinner LUS near term. Although this factor has never been associated with higher risk of uterine rupture, we need to consider this information in future researches and analyses of LUS thickness for the prediction of uterine rupture.