»  What is the difference between Monozygotic and Dizygotic Twins?  (Back)

Approximately one in every sixty births results in the delivery of twins. Twins are either dizygotic (commonly referred to as fraternal) or monozygotic (identical). Dizygotic twins are the result of two different eggs being fertilized by two separate sperm and resulting in two completely distinct and separate pregnancies in the womb at the same time. Monozygotic twins are the result of one egg fertilized by a single sperm. The fetus literally splits in two around the time that pregnancy is implanting in the womb (between the fourth and twelfth day of development). Monozygotic twinning accounts for approximately 30% of twin births while the remaining 70% of twins are dizygotic.

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