[Good results of single embryo transfer after in vitro fertilization. The first follow-up report after the introduction of a new regulatory guideline].

A legislation was issued by the Swedish National Board of Health from January 1st 2003, stating mandatory single embryo transfer (SET) after in vitro fertilization. Two embryos may, however, be transferred if the risk for twin pregnancy can be considered to be low. Over a period of one year, the rate of SET in our clinic was increased from 25% to 71% of all fresh embryo transfers. In spite of this, we maintained the overall viable pregnancy rate (34%). The twin pregnancy rate, on the other hand, decreased from 23% to 6%. The quality of the transferred embryo(s) was an important factor for success. Transfer of two embryos of good quality did not increase the pregnancy rate compared to transfer of one embryo of good quality but increased the risk for twin pregnancy only.