What are the different types of twins?

Twins can develop two different ways, when one fertilized egg divides into two, or when two separate eggs are fertilized at the same time, according to the National Institutes of HealthOff Site Icon (NIH). Two thirds of the time, an egg that divides produces two embryos that share a placenta, while two separate fertilized eggs produce embryos that have their own amniotic sac, according to the NIH.

Twins that are monozygotic – that develop from one fertilized egg – are identical and have the same DNA, according to the American Academy of PediatricsOff Site Icon (AAP). Twins that are dizygotic – developed from two fertilized eggs – are fraternal, and have their own DNA and amniotic sac, according to the AAP.

Ask your doctor about the different types of twins.

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