Is it true that twins run in families?
Answered by Jack Cleland, MD, Medical Group of the Carolinas — Pediatrics — North Grove
The answer is both yes and no.
Monozygotic or “identical” twins occur when a single fertilized egg divides into two separate embryos. This tends to be random around the world with no really known triggers.
Dizygotic or “fraternal” twins occur when two eggs happen to get fertilized at the same time. Fraternal twins not only run in families, but the rate also increases with fertility drugs, maternal age, race/geographic area, mom’s size, and diet.