How are twins formed?

If you're pregnant with twins it might come in handy to know how twins are formed. This way you'll know whether your twin babies are fraternal or identical.

By Kate Phillipa Clark

How are twins formed, you might wonder? It depends on whether your twins are identical or fraternal.

Identical twins

This type of twin is formed from one fertilized egg being split in two. The eggs develop into two individual embryos that share almost the same genetic material. When developing in the womb, identical twins can share or have their own individual placentas. The same goes with membranes. This sometimes makes it tricky to determine whether or not twin babies are identical or fraternal. Read more about how identical twins are formed to learn how to distinguish identical and fraternal twins from each other, or use our free Twin Test.

Fraternal twins

This type of twin is formed from two eggs being fertilized by two different sperm cells. Fraternal twins are genetically speaking like siblings – if the two sperm cells come from the same man, that is. They may feel a bit closer, though, as they share a womb and are born at about the same time. As with identical twins there are some patterns of fraternal twinning that are exceedingly rare – read about the different types of twins.

How are twins formed? We hope we’ve answered your questions. Otherwise post a reply below this article and we’ll do our best to assist you. 

About the Author

Kate Phillipa Clark

Kate Phillipa Clark has a bachelor in Journalism and an Executive Master in Corporate Communication. She is an identical twin and so is her father.


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