Information for Twins
Different types of twins - Identical (1 egg) OR Non-Identical (2 eggs)
There are two types of twins and they occur through two different processes.
Identical twins occur when the egg splits in two between the 1st and 14th day after conception. Each half of the egg has all the same genes so each baby is an identical copy of the other. Therefore, identical twins must always be either girl-girl pairs or boy-boy pairs.
Identical twinning is not hereditary, occurs randomly and for reasons we don’t clearly understand. One pregnancy in every 250 results in identical twins.
Non-identical twins occur when the mother releases two eggs in a cycle and both eggs are fertilised. The twins will have normal family resemblance to each other but can not be identical. These twins can be either girl-girl, boy-boy or girl-boy pairs.
Non-identical twinning is hereditary. There are usually other sets of twins somewhere in the family. Every one in 125 pregnancies results in non-identical twins.
