When are identical twins produced?

Identical twins form when one egg has been fertilised by one sperm and the zygote splits into two. This happens at the very earliest stage of development, when the zygote is no more than a cluster of a few cells. Dividing this early in conception means that each baby has exactly the same genetic information as the other.

Identical twins can also occur when one a woman has undergone fertility assistance and has had one fertilised egg returned to her uterus. If this egg then splits into two, an identical twin pregnancy can result.

Identical twins are not dependent on race, country or ethnicity. The odds of having identical twins are the same for every couple, in every pregnancy, wherever they live in the world.

Around one in every three sets of twins born is identical, and the remaining 2/3 is of the non-identical variety.
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There are 3 conditions for formation of twins
1) if two eggs are releases and is fertilised by different sperms.
2) if two sperms ferrilizes the egg at a time
3) by aplirring of zygote into two
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