Interaction Between Previous Cesarean Delivery and Anterior Placental Location in Persistent Low‐Positioned Placenta: A Retrospective Cohort Study

OBJECTIVES: To evaluate the interaction between previous Cesarean delivery and anterior placental location in persistent low-positioned placenta and the association between placental edge-to-internal-os distance and persistence among women with a low-lying placenta. METHODS: This single-center retrospective cohort study included 1508 singleton pregnancies with a low-positioned placenta identified during routine mid-trimester fetal ultrasound between 2020 and 2024. Multivariable analysis was used to evaluate factors associated with persistence and the interaction between previous Cesarean delivery and anterior placental location. Among women with a low-lying placenta, the association between placental edge-to-internal-os distance and persistence was also assessed. RESULTS: Previous Cesarean delivery and anterior placental location interacted significantly in relation to persistent low-positioned placenta (P for interaction = 0.003). The additive interaction risk difference was 20.0 percentage points (95% confidence interval [CI], 8.2-31.7). Placenta previa at the mid-trimester examination was associated with a higher risk of persistence than low-lying placenta (adjusted relative risk, 5.87; 95% CI, 4.95-6.96). Among women with a low-lying placenta, each 5-mm decrease in placental edge-to-internal-os distance was associated with a 63% higher risk of persistence (adjusted relative risk, 1.63; 95% CI, 1.45-1.83). CONCLUSIONS: Previous Cesarean delivery and anterior placental location interacted significantly in relation to persistent low-positioned placenta, and women with both factors present may warrant closer attention during follow-up. Considering these factors together with the type of low-positioned placenta and placental edge-to-internal-os distance may help refine risk assessment and inform subsequent ultrasound follow-up and clinical management.