Elective single versus double embryo transfer

This year, belatedly, Robert Edwards received the Nobel prize for his contribution to the development of human in vitro fertilisation. Louise Brown, the first child to be conceived after the technique was performed, was born in 1978. By the mid-1980s enough procedures were being performed around the world to get an idea of success rates, which became the early obsession. Around this time the main problem with the treatment also came to light—the increased incidence of high order multiple births. Twin birth is now the major problem, and in the linked study (doi:10.1136/bmj.c6945) McLernon and colleagues compared the effect of elective single embryo transfer versus double embryo transfer on pregnancy outcomes⇓.1

In the beginning, clinicians transferred too many embryos, often as many as they had available. The initial data seemed to support this practice, with lower pregnancy rates when only one or two embryos were transferred compared with three or more. It was less well understood that the outcome was worse when only one or two embryos were available than when a pool of embryos was available, from which the better ones could be selected.2 Gradually, the …