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%).