Originally Posted by ChristaN
I've heard that too. However in my family all five sets of twins are identical. We must be drinking some strange water or something ! I think that the idea is that fraternals run in families b/c it can be heriditary to release more than one egg at a time, but having an embryo split is purely chance.
I also have a friend who has tons of twins in her family and during each of her pregnancies she had herself checked for twins and the last pregnancy she got her fraternal twins. Who really knows?