Would legislation imposing single embryo transfer be a feasible way to reduce the rate of multiple pregnancies after IVF treatment?

Due to increased maternal and fetal risks, there is a strong opinion in favor of single embryo transfer (SET) in order to reduce the high multiple pregnancy rate after IVF. We have evaluated the effects on pregnancy rate and twinning of recent Swedish legislation on SET. The study comprised three embryo transfer (ET) periods: period I, autumn 2001-spring 2002 (n=609), with a double embryo transfer (DET) policy; period II, autumn 2002 (n=320), a transitional period; and period III, January-September 2003 (n=433), with a SET policy. During the three periods, the SET rates were 25.1, 55.5 and 72.7%, respectively (Kruskal-Wallis test P<0.0001). There was no difference in clinical pregnancy rates (33.3, 32.8 and 37.4%, respectively) (P=0.4), but the twinning rate was significantly lower in the third period (6.2 versus 22.6% in period I and 16.3% in period II) (P<0.005). After introducing a SET policy, the expected decline of twinning was met at an unchanged clinical pregnancy rate. Thus, the SET legislation had no negative consequences for the couples. On the contrary, the lower rate of twinning is expected to reduce the severity and rate of pregnancy complications after IVF. Whether legislation or voluntary SET is the most feasible way to proceed, in order to reduce the multiple pregnancy rates after IVF, can be debated.