Is there a cancer risk? The short answer is, we still don’t know. The ovaries produce the female sex hormones oestrogen and progesterone, and artificially raising their levels in the body could enhance the risk of developing hormone-related cancers such as breast or uterine (womb) cancer (BMJ, 1989; 299: 309-11).

There is no doubt that excess exogenous oestrogen (not made in the body naturally) causes cancer. There is substantial evidence that sex hormones are implicated in a number of women’s cancers, as they are the hormones that stimulate cell division in organs such as the breast, ovaries and lining of the womb.

In the US, it is now accepted that hormones account for more than 30 per cent of all cancers seen in American women (At Risk: Health, Safety & Environ-ment, 1998; 9 [Summer]: 201-27).

During IVF, hormone levels are sent sky high. In some instances, levels of these hormones more than double for up to three consecutive days.

There is an analogy here with the use of hormone replacement therapy, where large-scale studies like the Women’s Health Initiative in the US and the Million Women Study in the UK have now indisputably shown an increased risk of breast and ovarian cancer after a single year of HRT use (JAMA, 2002; 288: 321-33; Lancet, 2003; 362: 419-27).

Another possible reason for an increased risk of ovarian cancer in IVF is that ovarian stimulation results in a high number of eggs. One stimulated IVF cycle results in the equivalent number of eggs in a single month that would ordinarily take a woman’s body a year or even two to produce. Women can have as many as 20 goes with IVF, thereby producing between 200-500 eggs - equal to 20 years’ worth - in less than two years.

However, the research into the risks is, to say the least, conflicting. In one of the latest studies, researchers at La Trobe University in Carlton, Australia, carried out a series of observational studies on one of the largest sample sizes to date. They followed-up 29,700 women, treated at 10 Australian IVF centres before January 1994, for a period ranging from one to 22 years, with most followed-up for five to 10 years. Of these women, 20,656 had received fertility drugs during IVF (the ‘treated’ group) and 9044 had not (the ‘untreated’ group).

Although there was no significant difference in breast and ovarian cancer in the two groups during the study, more women than predicted in the treated group had a breast cancer diagnosed in the first year after treatment with fertility drugs - nearly double the predictions (Lancet, 1999; 354: 1586-90).

Nevertheless, another recent study arrived at a different conclusion. In this report, where investigators from the US and other countries collected data on infertility and fertility-drug use from eight case-control studies, women who had used fertility drugs were no more likely to develop ovarian cancer than those who had never used them. Every successful pregnancy reduced the risk of developing it later. Women who had spent more than five years unsuccessfully trying to conceive were at a 2.7-fold higher risk for ovarian cancer than those who tried for less than a year.

It may well be that infertility itself predisposes to ovarian or breast cancer, as all the women with unexplained infertility had more cancers of the ovary and uterus than predicted - whether or not they had treatment with fertility drugs. Endometriosis also appeared to be a risk factor (Lancet, 1999; 354: 1586-90; Am J Epidemiol, 2002; 155: 217-24).