[Single embryo transfer].

Thanks to assisted reproduction technology (ART) most couples with infertility can be helped today. Since the beginning of ART, however, two major problems have existed. In the first years of IVF more than one embryo was transferred in order to reach acceptable pregnancy rates, but this entails a risk of multiple pregnancy with all its morbidity and mortality due to premature birth. Also, studies comparing the outcome of children following ART with the outcome of children who were spontaneously conceived, showed that ART increased the risk of prematurity and low birth weight, even in singleton pregnancies. The transfer of just one embryo (single embryo transfer or SET) in IVF/ICSI treatment cycles appeared to be the only answer to the epidemic of multiple pregnancies. The studies which analyze the outcome of SET singletons are promising, since they suggest that a broader application of SET could have a positive influence on the outcome of pregnancies after ART as well.