Placental fusion

Last revised by Dr Jeremy Jones on 20 Sep 2021

Placental fusion is a phenomenon that can occur in a twin pregnancy. This can occur to varying degrees. Determination of chorionicity on ultrasound can sometimes be difficult if there has been a placental fusion. 

In a DCDA pregnancy, there are no vascular anastomoses between the twin placentae and with an equator marking a zone of disc fusion where there is a narrow band at the equator where chorionic vessels do not cross 4

In a MCDA pregnancy, multiple vascular anastomoses are usually present making the junction less distinct with examples of arterial to venous, arterial to arterial, or venous to venous connections being evident 4.

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