A new study on the effect of single embryo transfer (SET) on pregnancy rates has triggered further calls for the UK's Human Fertilisation and Embryology Authority (HFEA) to stick with its existing policy on this issue. The research, published in the journal Human Reproduction, shows that imposing a single embryo limit on all women undergoing fertility treatment - irrespective of their age or embryo quality - would halve the pregnancy rate per cycle of IVF.

In July 2005, the HFEA reviewed its guidelines on how many embryos can be implanted during IVF treatments. At the time, over 90 per cent of IVF cycles in the UK involved the transfer of two or three embryos. The HFEA was considering limiting IVF treatments to the transfer of a single embryo per cycle, as has been done in some other European countries. Current guidance, found in the HFEA Code of Practice, stipulates that clinics should transfer no more than two eggs or IVF embryos at a time to women under 40 years old and no more than three eggs or embryos to women older than 40.

In the latest study, carried out at the Academic Hospital in Maastricht, the researchers compared pregnancy rates in 308 women receiving IVF treatment. Half of the patients had a single embryo transferred, while the other half received two. The patients were randomly assigned to one group or the other, regardless of their age or the quality of their embryos. Another group of patients were treated according to the centre's current policy: 100 patients with a good chance of success received one embryo, while those with reduced chances (122) received two.

The pregnancy rate in the unselected patients was 40.3 per cent for women who received two embryos, and 21.4 per cent in the patients who received a single embryo. Transferring a single embryo cut the twin pregnancy rate from 21 per cent to zero. However, in the patients treated according to their predicted chances of success, the pregnancy rate was around 30 per cent - regardless of the number of embryos transferred. In the group who received two embryos, the twin pregnancy rate was around 13 per cent.

Dr Mohammed Taranissi, of the Assisted Reproduction and Gynaecology Centre in London, said the study showed that if a SET policy is introduced in the UK, there will be a 'severe impact' on pregnancy rate. Clare Brown, of the charity Infertility Network UK, said that 'patients feel the Government is already letting them down because they cannot get IVF on the NHS [National Health Service], so to then halve their chances of success is appalling'. She told the Sunday Telegraph that 'two embryos gives a better chance and people are prepared to take the risk of having twins, so they can have their family all in one go'.

However, other clinicians pointed to the health risks associated with multiple births as a reason to limit the numbers of embryos transferred. 'Sometimes you get triplets and if two of them are handicapped you think "Why did I do that?'" From a clinician's point of view it is terrible', said Professor Peter Braude, chairman of the HFEA's expert group on multiple births. A spokesman for the HFEA said it would look closely at the latest research, and was expecting a report from the panel at the end of the year.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.