Visibility and measurement of cesarean section scars in pregnancy: a reproducibility study.

OBJECTIVES: To evaluate the visibility of cesarean section (CS) scars by transvaginal sonography (TVS) in pregnant women, to apply a standardized approach for measuring CS scars and to test its reproducibility throughout the course of pregnancy. METHODS: In this observational cohort study, 320 consecutive pregnant women with a previous cesarean delivery were examined to assess scar visibility by two independent examiners. TVS was carried out at 11-13, 19-21 and 34-36 weeks' gestation. A scar was defined as visible when an area of hypoechogenicity representing myometrial discontinuity at the anterior wall of the lower uterine segment was identified. In a subset of patients (n = 111), visible scars were measured by two independent examiners in three dimensions: scar width, depth and length as well as the residual myometrial thickness (RMT). Descriptive analysis was used to assess scar visibility, and the intraclass correlation coefficient (ICC) was calculated to show the strength of absolute agreement between two examiners for scar measurements. For RMT, a cut-off of 2.4 mm was used and measurement agreement was assessed using Cohen's kappa coefficient. RESULTS: The scar was visible in 284/320 cases (88.8%). Visible scars were significantly associated with anteverted uteri (P < 0.0001). Both examiners had 100% agreement on scar visibility at 12 and 20 weeks' gestation, while agreement was 96% at 34 weeks. The intra- and interobserver agreements for scar measurements were generally good (ICC 0.86 and 0.89, respectively). The kappa coefficient for the RMT was 0.27 in the first trimester, compared with 0.51 and 0.72 in the second and third trimesters, respectively. CONCLUSION: CS scars remain visible in the majority of women throughout pregnancy. They can be reproducibly measured in three dimensions when assessed by TVS in all trimesters of pregnancy. The agreement between two observers for CS scar measurement can be considered good for the first trimester, compared with relatively moderate agreement for the second and third trimesters.