1. Identical twins occur when one egg divides into two, so that the babies have the same genetic makeup. Fraternal twins occur when two separate eggs are fertilized. Like fraternal twins, identical twins normally have two separate amniotic sacs. It is extremely rare for these twins to share one sac, and dangerous, too, since the babies’ umbilical cords could get entangled during the pregnancy. Your girls could indeed be identical, especially if they look a great deal alike. The fact that they have the same blood type isn’t a clear indication, as it is quite common for siblings within any family to have the same blood type. The only way to know for certain is to have the girls genetically tested. Their doctor should be able to help you find out how to do this and the costs involved.

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Ask Tori RN®, by registered nurse and resident author of The Joy of Pregnancy, is a helpful and reassuring resource for parents-to-be.