Factors associated with lower uterine segment thickness near term in women with previous caesarean section

To estimate the association between potential influencing factors and lower uterine segment (LUS) thickness at term in women with previous Caesarean section.

We conducted a cohort study of women with previous low-transverse Caesarean section undergoing ultrasonographic measurement of LUS thickness between 35 and 38 weeks' gestation in a tertiary care centre between 2006 and 2009. Measurements of the full LUS thickness and the myometrial LUS thickness were performed both transabdominally and transvaginally. The thinnest measurements for both full and myometrial LUS thicknesses were considered dependent variables. Non-parametric analyses, multivariate linear regression analyses, and multivariate regression analyses were used to evaluate the relationships between LUS thickness and the potential influencing factors of maternal age, interdelivery interval, prior vaginal delivery, and several characteristics of the previous Caesarean section.

In 377 women who underwent measurement of LUS thickness, labour before previous Caesarean section was the only characteristic associated with a greater full LUS thickness (an additional 0.9 mm; 95% CI 0.5 to 1.2 mm) in multivariate linear regression analysis. Labour before previous Caesarean section (0.5 mm; 95% CI 0.2 to 0.7 mm) and the use of synthetic sutures (as opposed to catgut sutures) for the closure of the previous hysterotomy incision (0.3 mm; 95% CI 0.02 to 0.5 mm) were the only two variables significantly associated with a thicker myometrial LUS. In multivariate regression analysis, three factors were predictive of a full LUS thickness of > 2.3 mm: the presence of labour, a recurrent indication for Caesarean section, and the use of synthetic sutures for hysterotomy closure at previous Caesarean section (P < 0.05).

Labour at the time of previous Caesarean section is associated with a thicker LUS near term in the subsequent pregnancy. The use of synthetic sutures for hysterotomy closure is another factor potentially associated with a thicker LUS.