Impact of Labor at Prior Cesarean on Lower Uterine Segment Thickness in Subsequent Pregnancy

Objective: The objective of the study was to identify the factors associated with sonographic lower uterine segment (LUS) thickness near term in women with prior low transverse cesarean.

Study Design: A prospective cohort study of women with a single prior low transverse cesarean was conducted. LUS thickness was quantified by transabdominal ultrasound with repeated transvaginal measurement when necessary. The thinnest measurement was considered as the dependent variable. Potential related factors were evaluated with nonparametric analyses and multivariate logistic regressions.

Results: Two hundred thirty-five women were recruited at a mean gestational age of 36.7 +/- 1.3 weeks. The full LUS was thicker in women who had their previous cesarean during the latent phase (2.8 mm; interquartile [IQ], 2.0-3.3 mm) or the active phase of labor (3.1 mm; IQ 2.5-3.9 mm) than in women with previous cesarean prior to labor (2.4 mm; IQ 2.0-3.2 mm). The association remained significant after adjustment for potential confounders.

Conclusion: Presence of labor at previous cesarean is associated with a thicker LUS in a subsequent pregnancy.