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The Twin Placenta


Updated July 03, 2014

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Twin Placentas and Fetal Membranes
Mother and two week old fraternal twins.
Ruth Jenkinson/Science Photo Library/Getty Images
The placenta is the body's only disposable organ. The placenta, with the attached membranes (amnion and chorion), are designed to function as the home, filter and feeding mechanism for pregnancy. In a twin pregnancy, there are many more variables for a twin placenta and the fetal membranes.

Fraternal twins, also known as dizygotic twins since they come from two eggs and two sperm, always have their own placenta and surrounding sacs. About 70% of monozygotic twins, or single egg and single sperm made identical twins, will end up sharing a single placenta which can cause potential complications. The most problematic is also the least likely (about 1%) and affects only identical twins, is the combination of a single placenta and a single sac.

Zygosity refers to how many eggs were involved with the conception of your twins. One egg (ova) makes monozygotic or identical twins, but two eggs are a set of dizygotic or fraternal twins. Chorionicity talks about how the membranes are laid out.

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