Cesarean scar defects (CSDs) are disruptions in the myometrium at the site of a previous cesarean delivery and
have become a concern in reproductive medicine due to their impact on gynecological and reproductive health.
This cross-sectional study compared the diagnostic performance of three-dimensional transvaginal sonography
(3D-TVS) and three-dimensional saline infusion sonohysterography (3D-SIS) in detecting CSDs among 403
women with prior cesarean delivery. The primary outcome was the prevalence of CSDs detected by 3D-TVS
and 3D-SIS. Secondary outcomes included diagnostic agreement and the correlation of morphological param-
eters including defect length, width, residual myometrial thickness (RMT), and adjacent myometrial thick-
ness (AMT). CSD prevalence was 34.0% by 3D-TVS and 80.6% by 3D-SIS, demonstrating poor agreement
(κ=0.20). Sensitivity and specificity of 3D-TVS were 42.15 and 100%, respectively. Measurements from both
modalities were positively correlated (p<0.0001), showing strong correlation for RMT (r=0.60) and moderate
correlations for defect length (r=0.47), width (r=0.57), and AMT (r=0.49). These findings support a stream-
lined diagnostic approach: when CSD is detected by 3D-TVS, further 3D-SIS evaluation is likely unnecessary,
whereas a negative 3D-TVS finding in symptomatic patients may warrant subsequent 3D-SIS assessment to
reduce the risk of missed diagnoses.
Keywords Cesarean scar defect · Isthmocele · Transvaginal sonography · Sonohysterography · Three-
dimensional imaging