Placenta membranacea, also known as a placenta diffusa, is an extremely uncommon variation in placental morphology in which the placenta develops as a thin membranous structure occupying the entire periphery of the chorion.
The estimated incidence is ~1:20,000-40,000 pregnancies .
- abnormal placental adherence: reported in up to 30% of cases
In this situation all of the fetal membranes are covered by functioning villi and the placenta develops as a thin membranous structure occupying the entire periphery of the chorion. The placental mass can often be thin (1-2 cm 7,8) and even disrupted.
May be seen as a placenta which circumferentially covers most (partial) or all (complete) of the entire uterine wall. May also show accompanying placental thinning and/or disruption.
Recognised complications include: