Effective anatomical and functional status of the lower uterine segment at term: estimating the risk of uterine dehiscence by ultrasound.

OBJECTIVE: To define the role of lower uterine segment (LUS) evaluation at term. DESIGN: Observational case-control study. SETTING: University hospital. PATIENT(S): Ninety-four patients were divided into two groups. Group A consisted of 45 multiparous single fetus pregnant women with up to two previous cesarean sections (CS). Group B consisted of 49 multiparous pregnant women with up to three vaginal deliveries and no uterine scars. INTERVENTION(S): Total LUS and myometrial thickness were measured by sonogram in all patients before undergoing a CS. MAIN OUTCOME MEASURE(S): The primary outcome is a correlation between echographic measurements and features of the LUS at the time of CS. The secondary outcome is a definition of a correlation between the number of previous CS, interdelivery interval time, and features of the LUS (grades I-IV). RESULT(S): Sonographic measurements revealed significant differences in LUS size and myometrial thickness between the two groups. Grades III and IV of LUS were only observed in group A. An interdelivery interval <18 months, LUS thickness ≤ 3.0 mm, and myometrial thickness < 1.5 mm were statistically significant predictors of LUS grades III and IV. Number of previous CS showed no correlation with surgical LUS status. CONCLUSION(S): Sonographic evaluation of the LUS may be a noninvasive, reproducible, and safe technique for defining the risk of uterine dehiscence, with a sensitivity of 100% and specificity of 85% (positive predictive value, 45%; negative predictive value, 100%).