Incidentally Identified Basal Plate Myometrial Fibers and Hemorrhage Risk in the Subsequent Pregnancy

Background/Objectives: This study examines index pregnancies with histopathological diagnosis of placenta accreta, based on findings of basal plate myometrial fibers (BPMFs) without intervening decidua, and the risk of hemorrhagic morbidity and/or clinically adherent placenta in the subsequent pregnancy. Outcomes were compared between index pregnancies with incidental asymptomatic BPMF findings and those with symptoms based on hemorrhagic and placental factors. Methods: A retrospective cohort study was conducted at a large, integrated healthcare system from 2008 to 2019. All patients with an index finding of BPMF without intervening decidua and subsequent delivery of a live singleton were identified. Index pregnancies with BPMF were categorized as asymptomatic or symptomatic by the absence or presence of hemorrhagic morbidity and/or clinically adherent placenta. Rates of hemorrhagic morbidity and clinically adherent placenta in the subsequent pregnancy were compared among asymptomatic and symptomatic BPMF index pregnancies in bivariate analyses and multivariate models controlling for potential confounders. Results: A total of 140 patients were found to have BPMF and a subsequent delivery of a live singleton. Subsequent hemorrhagic morbidity/adherent placenta occurred in 28% of cases, with a lower incidence in asymptomatic patients (8% vs. 39%, p < 0.0001). Symptomatic BPMF was associated with increased odds of hemorrhagic morbidity/adherent placenta (aOR 10.2, 95% CI 2.7–38.4). Among 71 patients with subsequent placental pathology, 32% had recurrent BPMF, which correlated with higher morbidity compared to those without recurrence or those without placental pathology (61% vs. 40% vs. 9%, p < 0.0001). Conclusions: Incidentally identified BPMF was associated with a lower rate of subsequent hemorrhagic morbidity and/or adherent placenta compared to symptomatic BPMF. Symptomatic BPMF is highly associated with hemorrhagic morbidity and/or adherent placenta in the next pregnancy compared with incidentally identified BPMF, particularly if it is recurrent. These data can inform counseling and management of pregnant individuals with BPMF planning subsequent pregnancies.