It is widely known that fertility treatment can result in a greater likelihood of a multiple pregnancy. Quadruplets and higher-orders of multiples, although receiving lots of publicity, are rarely the result of IVF. Instead, they usually arise as a result of high dose fertility drugs combined with intra-uterine insemination (IUI). Twins and triplets however, are more common with IVF, with the chance of a multiple birth increasing from 3% in natural conception to 33% with IVF treatment. This is because more than one embryo can be placed in the womb to increase the chances of pregnancy. In the UK, many clinics operate with a strong ‘single embryo transfer’ policy in order to reduce the incidence of multiple births. There are many risks associated with the delivery of twins and so it is important to not unnecessarily return more than one embryo. Multiple-embryo transfers are therefore mostly recommended for difficult prognosis patients. Identical as well as non-identical twins are more likely to occur, possibly because of techniques associated with IVF such as ICSI when a sperm is injected into the sperm, and PGD when a cell is removed for inspection.