Embryo freezing safety concerns

Scientists in the United States claim that they have established a link between the use of frozen embryos during IVF treatment and ectopic pregnancies. They say that ectopic pregnancies - where the embryo implants in the wall of the Fallopian tube, rather than the lining of the uterus - are 17 times more likely in women who conceive after IVF using embryos thawed after being in frozen storage. Ectopic implantations always result in the loss of the pregnancy, and can be potentially fatal for the woman, as well as affecting her future chances of conceiving.

It was already known that the IVF procedure itself - where eggs and sperm are combined in the laboratory and a fertilised egg (embryo) is later transferred to the woman's womb - results in a greater number of ectopic pregnancies than natural conception. But the latest research seems to add fuel to growing concerns about the safety of embryo freezing, for the health of both the women using IVF and their children.

The new study, undertaken at Brown University and the Women and Infants Hospital in Providence, Rhode Island, US, was led by David Keefe. It followed observations made by one of his staff that ectopic pregnancies appeared to occur more frequently when frozen/thawed embryos are used. The research team compared the results of the fertility treatments they performed with fresh and frozen embryos between January 1998 and March 2002. They found that only nine out of 490 (1.8 per cent) implantations achieved using fresh embryos resulted in ectopic pregnancy, compared with six out of 19 pregnancies (31.6 per cent) where the embryos used had been frozen.

Dr Keefe presented the results of the study at the annual conference of the American Society of Reproductive Medicine held in San Antonio, Texas last week. He said that the study showed that further research on his initial findings was necessary, especially 'given their importance for patient counselling'. 'We've made the observation, now the burden is to figure out why', he said. But, he noted that the sample of women studied who were using frozen embryos was very small. A larger research group may not lead to such startling results.

Asked why he thought embryo freezing might increase the risk of ectopic pregnancy, Dr Keefe posited several theories. 'One possibility is that freezing and thawing slows the development of the embryo, so the normal timing is disrupted', he said, adding that 'another theory is that freezing and thawing alters the zona pellucida. This could change its adherence: it shouldn't be sticking in the tube'. Last month, Professor Lord Robert Winston, a UK fertility specialist, claimed that the embryo freezing procedure might affect gene expression in embryos. Dr Keefe, when asked whether he believed Winston's theory might be linked to his own, replied 'possibly, yes'. Gillian Lockwood, another UK fertility specialist, said that 'if these findings are true it is worrying', but pointed out that about 250,000 babies have so far been born from frozen embryos and that more research was needed before any link could be proved.

Richard Kennedy, from the British Fertility Society, said there was no reason to believe that a greater risk of ectopic pregnancy was attached to the use of frozen embryos: 'We have been using frozen embryos for 15 years and have carried out thousands of frozen embryo cycles', he said. He continued: 'Nobody has previously reported an increased risk from this type of technique'. Alison Cook, speaking for the UK's Human Fertilisation and Embryology Authority (HFEA), said the American study showed abnormally high rates. She questioned whether freezing protocols differed between the UK and the US.  'It's surprising', she said. 'I've never seen anything like it before'.