IVF and Multiples
In-Vitro Fertilisation is a process where a woman's egg is fertilised by a sperm in a lab and the resulting embryo is transferred to the woman's uterus
.The idea is that the embryo will implant itself in the uterus wall and develop into a fetus which can be carried full term.
Because IVF is such an expensive procedure, ideally it would work first time round. To increase the chance a successful pregnancy more than one of the fertilised eggs is usually inserted into the woman's uterus. Sometimes more than one embryo will manage to implant in the uterus. If this is the case and all the embryos develop into fetuses, non-identical twins/triplets/quads will be born (depending on how many separate embryos implanted).
In other cases only one embryo successfully implants but it splits into two resulting in identical twins (or triplets/quads etc if the egg splits into three or four or more!). The risk of an embryo dividing is higher after IVF treatment but it is not yet understood why.
Potentially both of these mechanisms might occur meaning that triplets are born with two being identical and the other not.
So, undergoing IVF treatment dramatically increases the likelihood of carrying multiples with about 25% of IVF patients having a multiple birth. In other words you are 20 times more likely to have a multiple pregnancy following IVF than if you conceived naturally.
Dizygotic (non-identical) twins are more common than monozygotic (identical) twins after IVF.