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Updated May 21, 2010

Definition: When monozygotic twins are contained in a shared chorion, they are referred to as monochorionic. The chorion is the outer membrane of the sac surrounding a fetus in utero. Monochorionic twins can be either monoamnionic or diamnionic.
Common Misspellings: monochronic, monochorionoc
During a twin pregnancy, it is important to determine the structure of the chorion. Twins that share a are considered monochorionic and may be at risk for complications, such as Twin to Twin Transfusion Syndrome.

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