Images in abnormal placenta: a rare case of "blood bag" formation in placenta membranacea.

Placenta membranacea is an uncommon placental anomaly. Here, we present the case of a 30-year-old primiparous woman admitted for thickened placenta and reduced amniotic fluid. A follow-up ultrasound, performed after 48 h, revealed that the placental parenchyma was thin and not adequately visualized, enclosing a substantial volume of flowing blood (150 mm), with an amniotic fluid index of 18 mm. An emergency cesarean section was promptly performed. Following fetal delivery, a substantial accumulation of dark red blood within the fetal membranes created a "blood bag", estimated at approximately 3000 ml. This observation aligned with the ultrasound findings, and both placental morphology and pathological results substantiated the diagnosis of placenta membranacea.