This study in Turkey evaluated the impact of age-based mandatory single-embryo transfer (SET) legislation with the subsequent increase in frozen-thawed embryo transfer (FT-ET) on pregnancy outcome of in vitro fertilization (IVF) patients. SET, FT-ET and double-embryo transfer were used in 5632 patients after legislation, while traditional IVF and FT-ET approach was used in 6029 patients before legislation. The cumulative pregnancy rate after legislation was slightly lower (38.2%) than before legislation (42.0%) but not significantly so. The single pregnancy rate for SET and traditional IVF were similar between the 2 groups (37.8% versus 28.7%), while multiple pregnancy rates were significantly higher before than after legislation (13.7% versus 0.3%). For FT-ET, the number of cycles was significantly higher after legislation (862 versus 616). SET yielded similar results to traditional IVF. In order to reduce multiple pregnancies without significantly decreasing pregnancy rates, SET might be a successful strategy.