Zonary placenta

Last revised by Dr Jeremy Jones on 20 Sep 2021

A zonary placenta also known as a ring-shaped placenta or annular placenta is an extremely rare variation in placental morphology where the placenta can appear as an annular ring. It can be a complete ring of placental tissue, but more often, tissue atrophy to part of the ring can results in a horseshoe shape placenta.

Epidemiology

Reported incidence is less than 1 in 6000 1.

Complications

The ring-shaped placenta can cause antepartum and postpartum bleeding, as well as fetal growth restriction 3.

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