Single-embryo transfer.

The high incidence of multiple pregnancy is a major side effect of assisted reproductive technology that has recently given rise to justified criticism from different sides. The reasons for the high incidence of multiple pregnancies are discussed and a brief review is given of the steps that have been proposed to solve or at least reduce the problem. In this article, attention is particularly focused on the prevention of twin pregnancies because in terms of perinatal morbidity and associated costs, they outweigh the effect of high-order multiple pregnancies when expressed in absolute figures. The only efficacious measure to reduce the incidence of twin pregnancies is a policy of single-embryo transfer. We report on our experience with elective single-embryo transfer in good prognosis patients (age <37 years, first two in vitro fertilization (IVF) cycles and at least two embryos of high quality). About one-third of the couples meeting these criteria agreed to have a single embryo transferred, at least during their first IVF cycle. Pregnancy rates in women who had an elective single-embryo transfer (more than one high-quality embryo available) were only slightly lower than those in the group with elective double (i.e., more than two high-quality embryos available) transfer (37.9 vs. 40.0%) but the incidence of twins was 0.0 versus 27.1%. This strategy resulted in a substantial decrease of the twin pregnancy rate from 27.0 to 14.9%, without affecting the overall pregnancy rate. The conditions that are to be fulfilled before this policy can and will be applied on a large scale are discussed.