What about the remaining twins since single-embryo transfer? How far can (should) we go?

Single-embryo transfer (SET) and more specifically elective SET (eSET) have taken their place in good clinical IVF/ICSI practice. After the initial cautious search for the characteristics of the twin-prone patient and of the selection of the embryo with the highest implantation potential many centres have embarked on the (progressive) implementation of SET, either by conviction or forced by legislation or both. It was only because the ongoing pregnancy rates remained largely unaffected that SET was accepted. Generally speaking, it can be said that the twinning rate after IVF/ICSI has dropped by at least 50% simply by transferring only one good-quality embryo in the first and second fresh IVF/ICSI cycles in young women, without decrease in the overall pregnancy rate. Preventing 'the second half' of IVF/ICSI twins constitutes another and probably tougher challenge because the target group is a heterogeneous mix consisting of patients in very different clinical situations. Can we expand our experience for further twin prevention to women of older age and to cycles of higher rank without a significant drop in pregnancy rates? Can we extend it to more cryopreservation cycles? To have an idea of future target groups for increased application of SET, we analysed the remaining twins after double-embryo transfer (DET), and from these data we suggest expanding the eSET policy to women <38 years of age until the third cycle and to cryopreservation cycles.