A study into the potential effects of transferring a single embryo (SET) into the womb during IVF treatment has revealed that success rates are likely to drop as a result. The study, published in the journal Human Reproduction, was undertaken by Dr Daniel Brison and his colleagues at the UK's University of Manchester and explores the practicalities of implementing the Human Fertilisation and Embryology Authority (HFEA)'s latest initiative to attempt to reduce the numbers of multiple births resulting from IVF treatment.
Dr Brison supports SET on the grounds that multiple births are the greatest risks faced by IVF patients and their babies. In many countries, multiple embryos are often transferred in order to maximise the chance of pregnancy. In the UK, the most recent 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. Implanting more than one embryo can increase the chance of having a successful outcome - but it also increases the incidence of twin births, which puts increased strain on intensive care and neonatal units. A campaign called 'One at a Time' was launched in June this year and, in September, The British Fertility Society (BFS) and the Association of Clinical Embryologists (ACE) introduced new guidelines aimed at reducing the number of multiple births, recommending that a SET policy should be adopted for women under 37.
Dr Brison commented that 'single-embryo transfer is the right way forward, but we have to fund more than one cycle', highlighting the fact that only 15 per cent of NHS trusts provide the full three state-funded cycles recommended by the National Institute of Health and Clinical Excellence (NICE) in 2004.
The government aims to cut multiple births from one in four to one in ten by 2012. Dr Brison's study constructed a model based on these figures which show that in order to achieve that target, the equivalent of 55 per cent of patients at St Mary's Hospital in Manchester would have to have SET thereby bringing the success rate down by about 20 per cent.
The paper suggests that in order to limit a negative impact on pregnancy rates, women would need to be carefully selected according to an analysis of their embryos, their age and their hormone levels. Professor Peter Braude of Kings College London, leader of the group who devised the single-embryo policy, insisted that women could be chosen who would not be disadvantaged by the policy. 'It doesn't reduce pregnancy rates in women who are most likely to get pregnant, and who are also most likely to have twins,' he said, adding 'we have never said that a single embryo is right for every woman and the 10 per cent target is an aspiration'. He suggests that by identifying women most likely to have multiple births, incidences can be reduced without having a detrimental effect on pregnancy rates.
Dr Brison emphasised that implementation of the HFEA's policy needed to be backed up by better NHS access to IVF, particularly follow-up treatments using frozen embryos. Evidence from Scandinavia and Kings College London shows that a woman's chances of conceiving are not necessarily reduced by single-embryo transfer if the cycle is then repeated using another frozen embryo.