Never implant more than two IVF embryos

Either one or two embryos may be the best number to implant during assisted conception, depending on the woman being treated – but never three or more, say researchers. In their study, published online first in The Lancet, they used data from the UK Human Fertilisation and Embryology Authority to investigate the consequences of implanting different numbers of embryos in women undergoing in vitro fertilisation.

The study authors analysed HFEA data on 124,148 cycles of IVF, resulting in 33,514 livebirths. They compared rates of live birth, multiple births, low birthweight (<2.5kg), preterm birth (<37 weeks), and severe preterm birth (<33 weeks) in women younger than 40 years and in women at least 40 years old.

Younger women had a higher livebirth rate than older women regardless of how many embryos were transferred.

In both age groups, the livebirth rate was greater when two rather than one embryo was transferred. Transferring three embryos was no more successful than transferring two embryos in older women, and reduced the livebirth rate in younger women.

All adverse perinatal outcomes were more likely if women had two or three embryos transferred, rather than just one – and the risk of severe preterm birth was especially increased when three were transferred.

Transferring two embryos was less likely to result in multiple birth, low birthweight, preterm or sever preterm birth in older women than it was in younger women, which the researchers said was largely explained by older women’s lower likelihood of being able to maintain twin/multiple pregnancies.

They said: “Our findings provide some support for the transfer of two embryos in women older than 40 years, because the risks of preterm and low birthweight were lower than those in younger women.

“In older and younger women, the transfer of two embryos was associated with greatest livebirth rates … A clear implication of our study, is that transfer of three embryos should no longer be supported in women of any age.”

They added: “In view of these findings and previous findings, we conclude that no more than two embryos should be transferred into women of any age, but greater freedom should be given to clinicians and patients to decide whether to transfer one or two embryos, according to prognostic indicators, such as maternal age.”

The author of an accompanying comment agreed, but stressed: “Patients with medical or obstetric contraindications to twin pregnancies should receive no more than one embryo, irrespective of age or other prognostic factors.”