Twins: What are your chances of having a second set?
I am a mother of identical twin girls and I want to have another baby. What are my chances of having twins again?Question:
There are two types of twinning -- monozygotic (identical) and dizygotic (fraternal) twins. The frequency of identical twins across the world is approximately one set per 250 births and is generally not dependent on race, heredity, age nor parity (number of pregnancies). Ovulation induction doubles the incidence of this type of twinning.
Fraternal twin conception is influenced by race, heredity, maternal age, parity and, especially, fertility drugs. Regarding heredity, the mother is most responsible for this. In one study, women who themselves were fraternal twins gave birth to twins at a rate of one set per 126 pregnancies. In another study, one mother of twins out of every 25 (four percent) was also a twin, but only one out of 60 (just under two percent) of their fathers was a twin.
As maternal age and parity increase, so does the incidence of twinning. There is also a tendency for fraternal twins to repeat in families. If the firstborn are twins of this type, you are about five times more likely to repeat twinning with the next pregnancy than would be true in the general population.
The book, "Having Twins" by Elizabeth Noble is an excellent resource.