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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.
- 1. Živković N, Krezo S, Matijević R, Živković K. Vaginal delivery through annular placenta -- case report. (2013) Croatian medical journal. 54 (2): 203-5. doi:10.3325/cmj.2013.54.203 - Pubmed
- 2. Steemers NY, De Rop C, Van Assche A. Zonary placenta. (1995) International journal of gynaecology and obstetrics: the official organ of the International Federation of Gynaecology and Obstetrics. 51 (3): 251-3. doi:10.1016/0020-7292(95)80020-4 - Pubmed
- 3. Kimberly M. Rathbun, Jason P. Hildebrand. Placenta Abnormalities. (2020) Pubmed