Fertility-boosting drugs could more than double the risk of subsequent offspring developing childhood leukaemia, acadmics warn today.
Every year tens of thousands of women in Britain undergo fertility treatment, that usually involves them receiving drugs to prompt their ovaries into producing more eggs. More than 13,000 babies are born annually thanks to assisted fertility technology.
No study has yet found convincing evidence suggesting that fertility treatment leads to babies that are any less healthy than those conceived naturally.
However, French researchers will tell a conference in London today they believe there is an association between the use of ovarian stimulation drugs and two types of childhood leukaemia.
Specifically, they have calculated that their use is associated with a 2.6-fold increase in the risk of developing the most common form of childhood leukaemia, called acute lymphoblastic leukaemia (ALL), and a 2.3-fold increase in the risk of developing a rarer type, called acute myeloid leukaemia (AML).
However, leukaemia experts say the research does not prove the drugs trigger cancer, and emphasise that - even if proved - any increase in risk is small in absolute terms.
The study looked at 764 French children diagnosed with acute leukaemia and 1,681 children who had not. Researchers asked their mothers for details of fertility problems and if they had sought fertility treatment, including whether the women had been treated with specific methods including IVF, artificial insemination or ovarian stimulation drugs.
Dr Jéremié Rudant, of the Centre for Research in Epidemiology and Population Health, INSERM, Villejuif, France, who led the research, said: "Previous studies have suggested a link between infertility treatments and acute childhood leukaemia, but there haven’t been many studies, most of them have been small, and they focused either on IVF or hormonal treatment.
"Our study was much larger and it’s the first time that a specific increased risk linked to fertility drugs has been found."
He accepted the study did not prove that fertility drugs caused cases of childhood leukaemia: "More research is now needed to investigate more closely the link between specific types of fertility drugs and what role the underlying causes of infertility may play in the potential development of childhood leukaemia."
The study also found that children of parents who struggled to conceive naturally - taking at least a year to do so - were 50 per cent more likely to develop ALL than children of fertile couples.
Oddly, it found no increase in the risk in children whose mothers had undergone IVF - even though almost all such women will have received ovarian stimulation drugs - or those who were artificially inseminated.
The research is being presented at the Childhood Cancer 2012 conference in London. It has not yet appeared in a peer-reviewed journal.
Ken Campbell, of the charity Leukaemia & Lymphoma Research, said it was "plausible" that the drugs could make pre-natal conditions more conducive for the later development of childhood leukaemia. However, he urged caution.
He said: "This research is a long way from proving that A causes B. There are several alternative explanations."
The finding could be the result of methodological problems, he said, or that children of parents who had fertility treatment had a greater underlying chance of developing leukaemia for genetic reasons.
Even it was proved that the drugs had an effect, he said the absolute increase in risk was small - raising it from about 1 in 2,000 to 1 in 1,000.
"99.9 per cent of women who undergo ovarian stimulation also have IVF," he said.
"There's no scienfitic evidence presented here to say there's a link [between the drugs and leukaemia]," he added.