Prevention of multiple pregnancies in assisted reproduction

Abstract

The incidence of multiple births has increased parallel with the success of assisted reproduction treatments (ART) mainly because of the multiple embryo transfer. As a response to the increased multiple birth rate, the number of embryos transferred was reduced in 1992-1994 from three or more to two in many European countries. After that, a dramatic drop in the number of triplet and higher-order pregnancies was seen, but the twin rate still remained high. According to the European registers by ESHRE, in 2001 still 34.4% of children conceived with ART originated from multiple pregnancies, of which 94% were twin pregnancies. Obstetric and perinatal complications affect twins more often than singletons, contributing to increased health risk of the mother of twins and the children born as twins. In addition to the medical complications, twin families are at a greater risk for psychosocial burden. From the health-economic point of view, cost impact for twins is threefold to that of singletons. Recently, the standards of success of infertility treatment have been widely debated in journals of reproductive medicine. The general conclusion from this debate is that both the delivery rate per treatment and the final outcome of the pregnancy should be considered when the success of ART is reported. The high iatrogenic twin rate resulting from ART still offers the infertility treatment providers a challenge to strive for minimizing the number of ART-related twins. The most efficient way to reduce twin rate in ART is single embryo transfer (SET). However, the worry about impairment of delivery rate if only one embryo is transferred has hampered the acceptance of SET. The four randomised controlled trials and some retrospective cohort studies published until now have confirmed the effectiveness of elective single embryo transfer (eSET) in reducing the twin rate below 10%. In addition, highly acceptable delivery rate is achieved with eSET. The final results of eSET are most obviously further improved by transfer of frozen-thawed embryos. The experience of eSET until now encourages mowing towards an individualised embryo transfer policy, where eSET is performed in good prognosis patients at high risk for a twin pregnancy when two embryos would be transferred. The aim of this article is to review studies about eSET as a method to prevent ART-related twin pregnancies and the ways used in nationwide implementation of eSET in Finland, Belgium and Sweden. © European Board and College of Obstetrics and Gynaecology 2005.