Let’s try to understand how the multiple pregnancy or how the twin pregnancy is formed. We all know that the sperm unites with the egg and forms the zygote and the zygote keeps on multiplying and undergoes series or stages of the development and forms the embryo. So in twin pregnancy what happens is when there is two types of the twin pregnancy, one is the dizygotic twins and one is the monozygotic twin. Zygocity is refers to the number of eggs from which the baby is formed. So as the name itself indicates that if it is a dizygotic twins, there are two separate eggs that are fertilised by two separate sperms and each one developing into a separate embryo. So that is called as the dizygotic twins and which is common like they are more or less siblings and they may not be of the same sex and there will be having different blood groups and they will be having a different architecture of growth pattern and that is called as non identical twins or fraternal twins or the dizygotic twins and this is very common and this type of twins shows a varied pattern and the incidence of dizygotic twins is increasing because of the increase in pregnancy is happening because of the IVF treatment and also these type of twins show variation in terms of the maternal age and also the parity and also the geographic distribution and also the ethnicity . So these dizygotic twins are more common in women who are of the higher age group and in those women whom we call it as multiparous, those who have had many children and who have had a family history of twins, especially on the maternal side.
