Women who undergo fertility treatment are four times more likely to have a stillborn baby than those who conceive naturally or use other methods, according to a new study. Dr Kirsten Wisborg and colleagues at Aarhus University Hospital in Aarhus, Denmark, found that the risks were 'significantly' higher for women who had in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) compared to unassisted pregnancies or those following other assisted reproductive treatments. The findings were published online in the journal Human Reproduction.

Dr Wisborg reassured women that the risk of stillbirth following fertility treatment is 'still very low' and said that the researchers do not know whether the increased risk is due to the fertility treatment or to unknown variables affecting couples who seek such therapy. She explained that the similar results for women who conceived naturally or after hormone treatment could indicate that the higher risk 'is not explained by infertility and may be due to other factors, such as the technology involved in IVF/ICSI'.

The researchers used data from the Aarhus Birth Cohort to analyse the pregnancies and outcomes of over 20,000 women from 1989 to 2006. They looked at the womens' age, education, smoking and drinking habits, and the time taken for them to become pregnant. The rate of stillbirths among those who had IVF or ICSI was found to be 16.2 per 1,000, compared to 3.7 per 1,000 for those who became pregnant naturally within one year, and 5.4 per 1,000 for those who took longer than a year. The still birth rate was lowest for those who received hormone treatment to stimulate egg production, at 2.3 per 1000.

However, Swedish research, published earlier this month, found no such link between IVF/ICSI and risk of stillbirth. Professor Karl Nygren and his team at the IVF and Fertility Clinic in Sofiahammet Hospital, Stockholm, conducted a similar, larger study of more than 27,000 women who gave birth following fertility treatment during a 25-year period. They found that the stillbirth rate among this group did not significantly differ from the general population. 'I don't know why the two studies should have such different findings, but couples should be reassured that the risk of stillbirths is low', said Professor Nygren. Dr Wisborg added: 'the results from the Swedish study and from our study should be interpreted with caution'.