How common is it for a woman to have identical quadruplets?
Dr. Abbasi: This is a really rare event. Spontaneous identical quadruplets occur in about 1 in 13 million pregnancies. By contrast, 1 in 100 pregnancies produce twins. What causes a woman to have identical quads? Dr. Abbasi: What happens [with identical twins] is that just before the embryo implants, it splits into two. And because embryo cells (at this stage of development) are “totipotent” [i.e. able to form an entire organism] each one can replicate itself into a completely new embryo, which eventually becomes an identical twin. Identical quadruplets result from the embryo splitting 4 times by chance – which is extremely unlikely to happen in one embryo. While we know the cause of the twinning (the division of the embryo at a very early stage) we don’t know the trigger behind the spontaneous splitting. When we do embryo (blastocyst) transfers with in vitro fertilization (IVF) we may implant 2 embryos and get 3 babies because one of those embryos splits. Do certain women have a highe
