Basal Plate Myometrial Fibers and Hypertensive Disorders of Pregnancy: A Case-Control Study.

Introduction Basal plate myometrium (BPMYO), the pathological presence of myometrial fibers in the basal plate, is a common finding on pathological examination of the placenta, yet its clinical correlates are not well studied. As myometrial fibers are frequently located in proximity to poorly converted maternal spiral arteries, our objective was to determine whether BPMYO is associated with hypertensive disorders of pregnancy (HDP), a well-known clinical sequela of abnormal maternal artery remodeling. Methods This case-control study included women who delivered a live-born singleton gestation whose placentas were sent for pathological examination. Cases were women with HDP (gestational hypertension, preeclampsia, or HELLP syndrome) as defined by American College of Obstetricians and Gynecologists. Controls were women without HDP. Women with chronic hypertension were excluded. The primary outcome was the presence of BPMYO. Secondary outcomes included the pathologic stage of BPMYO and the incidence of pathologically defined accreta. Each outcome was compared between cases and controls in bivariable and multivariable analyses. Results Of the 306 women who met inclusion criteria, 230 (75%) had HDP. BPMYO was present in 99 (32%) of placentas. Compared to controls, cases were younger, had higher body mass index, and were more likely to have diabetes, be nulliparous, deliver preterm, and have had a prior cesarean. There were no differences in the incidence of BPMYO, stage of BPMYO, or incidence of pathologically defined accreta between cases and controls. These findings persisted after controlling for potential confounders. Conclusions Although BPMYO may be more common in the setting of abnormal placental vasculature, there is no significant association between BPMYO and HDP.