Women who conceive using fertility treatment run a fourfold higher risk of a stillbirth, warn researchers.

They found extra risk for women having in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) compared with women getting pregnant naturally or using other treatments.

The study comes after a leading expert claimed Britain faces an infertility timebomb because a generation of babies may have inherited their parents' inability to conceive.

IVF pioneer Dr Andre van Steirteghem told a US conference that more than 260,000 children born from IVF treatments in the UK are at greater risk of health problems.

In a new study from Denmark, specialists say a small extra risk of stillbirth could be caused by the technology rather than fertility problems being experienced by couples having treatment.

Dr Kirsten Wisborg, who led the study, said 'Until now, there has been speculation that the increased risk of adverse outcomes, such as stillbirths, in assisted reproduction might be due to factors related to the underlying infertility of the couples.

'However, we found the risk was similar between sub-fertile couples, women who had conceived after non-IVF fertility treatment and fertile couples.

'This may indicate that the increased risk of stillbirth is not explained by infertility and may be due to other, as yet unexplained factors, such as the technology involved in IVF/ICSI or some physiological difference in the couples that require IVF/ICSI.

'It is important to remember that the risk of stillbirth is still very low among women pregnant after IVF/ICSI' she added.

Dr Wisborg and colleagues at Aarhus University Hospital analysed data on women booked for delivery between August 1989 and October 2006.

Out of a total of 20,166 singleton, first-time pregnancies, 16,525 (82 per cent) were conceived spontaneously after less than 12 months, 2,020 (10 per cent) after more than a year of trying (classified as sub-fertile), 879 (4 per cent) conceived after non-IVF fertility treatment and 742 (4 per cent) conceived after IVF/ICSI.

There was a total of 86 stillbirths, giving an overall risk of stillbirth of 4.3 per thousand pregnancies, says the study published in the medical journal Human Reproduction.

The risk of stillbirth in women who conceived after IVF/ICSI was 16.2 per thousand.

However, Dr Karl Nygren, associate professor at the IVF and Fertility Clinic, Sofiahammet Hospital, Stockholm, Sweden, said his team had failed to find such a risk in a similar study of more than 27,000 women having IVF.

He said 'We compared outcomes from pregnancies after IVF/ICSI with a control group of 2,603,601 spontaneous pregnancies.

'We found no increase in stillbirths from IVF/ICSI treatment in this larger group, and this contrasts with the Danish study that found a four-fold increase in the risk of stillbirths between the IVF/ICSI pregnancies and spontaneous pregnancies.