Two embryos is optimum number for safe and effective IVF treatment, say researchers

Currently in the UK, women over 40 years old are allowed to have three embryos used in an IVF treatment cycle, but the research published in The Lancet says the chances of success are no greater than for two while the risk of complications is higher.

The finding is likely to result in new UK guidelines for IVF treatment recommending using no more than two embryos in any one cycle of treatment, and similar recommendations being made in other parts of the world.

A major complication of IVF treatment is multiple pregnancy – the birth of twins or triplets – due to the placement of more than one embryo during treatment.

Currently around 40 per cent of US and 21 per cent of European IVF treatment cycles have three or more embryos transferred and around 20-30 per cent of IVF births result in multiple pregnancy

However, multiple pregnancy carries risks such as higher rates of pre-eclampsia, premature birth, caesarean section and blood loss.

The UK Human Fertilisation and Embryology Authority (HFEA) has set a target for all IVF clinics in the UK to reduce the multiple pregnancy rate of treatment to 10 per cent.

The study conducted by Professor Scott Nelson, Muirhead Chair of Reproductive & Maternal Medicine, in the School of Medicine, and Professor Debbie Lawlor, Medical Research Council Centre for Causal Analysis in Translational Epidemiology, Bristol, investigated whether the transfer of just one embryo in IVF treatment would be an effective method of reducing these risks.

Prof Nelson said: “Given the maternal and neonatal risks and associated socioeconomic cost of multiple pregnancy, the use of a single embryo in IVF treatment has been proposed.

“Countries such as Sweden and Belgium have adopted the single embryo approach which has resulted in a decrease in multiple births while maintaining a high birth rate.”

The researchers analysed 124,148 treatment cycles which resulted in 35,514 live births, and looked at five factors when comparing the results of transferring one, two or three embryos during treatment: live birth rate, multiple birth rate, preterm birth rate, severe preterm and low birthweight – and how these vary between women younger or older than 40 years.

The results revealed:

  • the rate of live births was lower for women over 40 years of age, regardless of how many embryos were transferred.
  • In women of all ages, the live birth rate was higher when two embryos were used, rather than one, with no difference when three were used.
  • The transfer of two embryos, rather than one, is less likely to result in pre-term or low birthweight in older woman compared with younger women
  • Three embryos do not increase the chances of live birth at any age and is associated with similar or worse outcomes when using two embryos.

Prof Nelson added: “With around 30 per cent of women in the UK who receive IVF treatment being over 37 years of age, this study demonstrates the most effective and safest way of conducting that treatment. It will also help women of all ages make a more informed decision on how many embryos to transfer for their own treatment.

“Given the drive to reduce multiple pregnancy by HFEA, this research demonstrates that two embryos should be the maximal number transferred during IVF treatment.

“Our results further highlight the importance of age with respect to the likely success of IVF. Couples need to understand that delaying childbirth until older ages of the mother may make it difficult to conceive and harder for IVF to be successful.

“For doctors seeing a new couple with infertility moving to IVF sooner rather than later is critical particularly when  the woman is 36 years of age rather than for example 26 years.”

Notes to Editors

For more information contact Stuart Forsyth in the University of Glasgow Media Relations Office on 0141 330 4831 or email [email protected]