ABSTRACT

The negative outcome in IVF children is mainly due to the increased risk of multiple pregnancy and the associated risk of prematurity, and it is urgent to decrease the rate of multiple birth after IVF, at the same time aiming at preventing the pregnancy rate from falling. The most important factor influencing the rate of multiple birth is the number of embryos transferred, which has gradually decreased but still shows a wide range worldwide. Several reports aiming at reducing the multiple birth rate by transferring two instead of three embryos, published during the 1990s, showed that the pregnancy rate was unaffected while the rate of multiple pregnancy decreased. In one of the largest studies, using the national British IVF database3, it was demonstrated within different age groups that only the multiple birth rate and not the overall birth rate increased when three instead of two embryos were transferred, if more than four

pregnancy rate of 35-40% and a live birth rate of approximately 25% per transfer. This routine was introduced in 1993 and resulted in the maintenance of a stable pregnancy rate, while triplets almost disappeared, but the twin rate remained unchanged at around 25%. Twin pregnancies are still associated with an increased risk of prematurity and there is an obvious need further to reduce the rate of multiple births.