How do Twins Develop?

Identical twins form when the woman's fertilized egg splits into 2 pieces. Fraternal twins are formed when 2 different sperm develop with 2 different eggs. Nobody knows why this occurs, it could be genetic or from age but it always seems like a miracle.. You can find more information here: http://pregnant.thebump.com/pregnancy/first-trimester/qa/how-do-twins-develop.aspx
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