Myometrial fibers in the placental basal plate can confirm but do not necessarily indicate clinical placenta accreta.

Placental basal plate myometrial fibers reflect mild placenta accreta. We tested the hypotheses that a macroscopically disrupted area relates to an area where the placenta is focally adherent and that the incidence of placenta accreta is higher than stated in the literature. Sagittal blocks were taken from the basal plate from macroscopically intact, disrupted, and mixed (viz, at the junction of intactness and disruption) areas, together with an en face block from 90 singleton placentas. Histologic examination revealed that 11 of 23 placentas with a macroscopically disrupted maternal surface and 16 of 67 with a macroscopically intact maternal surface had placental basal plate myometrial fibers, a significant difference. More cases were detected with sampling from the mixed than from the intact area, while sampling from the wholly disrupted area was unrewarding. The en face block also was helpful for detecting myometrial fibers. Extensive and selective sampling of the basal plate revealed a much higher incidence of placental basal plate myometrial fibers. Clinical chart review affirmed that their presence can confirm but does not necessarily correlate with a clinical diagnosis of mild placenta accreta.