Zonary placenta

Last revised by David Luong on 6 Feb 2022

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 result in a horseshoe shape placenta.


Reported incidence is less than 1 in 6000 1.


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

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