[Transfer of only a single embryo in in-vitro fertilisation]

In order to obtain high pregnancy rates per IVF cycle, ovarian stimulation is employed to produce multiple embryos. The best embryos are transferred into the uterus and the remainder are frozen for possible use in later cycles. Despite limiting the number of transferred embryos, more than half of all IVF babies are the result of multiple pregnancies. The associated morbidity and costs have led to calls for the adoption of single embryo transfer. New techniques such as pre-implantation genetic screening for aneuploidy have enabled better embryo selection with optimal chances of a healthy child. Milder ovarian stimulation protocols may further reduce the morbidity and costs of IVF cycles. Improved cryopreservation techniques should improve the chances of pregnancies in subsequent cycles using excess embryos. The definition of success in IVF should be changed from number of children per IVF cycle to number of children born after singleton pregnancies per IVF treatment started.