Stage 2 Basal Plate Myometrial Fibers in Delivered Placentas: Frequent Placenta Retention but Rarely Indicative of Clinical Placenta Accreta Spectrum

We describe the clinical characteristics of patients with Stage 2 Basal plate myometrial fibers (BPMF), a histologic lesion resembling Placenta accreta spectrum (PAS).

This is a retrospective analysis of patients sequentially diagnosed with BPMF. Clinical variables: indication for placenta examination, intrapartum hemorrhage, retained placenta, manual extraction, and surgical intervention. Histologic variables followed Amsterdam Placental Classification with additional description of local inflammation, excess fibrin deposition, and smooth muscle injury.

Of 121 patients with BPMF, only 5 (4.1%) had clinical suspicion for PAS. Surgical intervention consistent with FIGO definition of PAS was required in 24 (19.8%). Intrapartum use of blood products was seen in only 8 (6.6%), with estimated blood loss greater than 2 L in 6 (5 %). Among the most common indication for pathology examination were "Retained/adherent placenta" and "Manual extraction" in 52 (43.0%) and 20 (16.5%). Manual extraction was performed in 47 (39%). We found no clinical association with histologic findings other than BPMF.

While BPMF often coincides with partial placental retention at delivery, only 1 in 5 cases met FIGO criteria for PAS and serious hemorrhage was rare.