A team of scientists funded by the Cancer Research Campaign will analyse data from 2,700 infertile women recorded between 1963 and 1993.

Ovarian cancer is a particulary dangerous disease because there are no symptoms in its early stages.

Most women are not diagnosed until they are in an advanced stage and survival rates are poor.

The average woman has a one in 56 risk of developing ovarian cancer in her lifetime.

In the UK, 4,000 women die of ovarian cancer each year. Nearly 6,000 women are diagnosed with the disease annually.

Two US studies have suggested that women who had difficulty conceiving and were given fertility drugs to stimulate their ovaries to produce more eggs had an increased risk of ovarian cancer.

The drug clomiphene citrate has been associated with a higher risk, and the Committee on Safety of Medicines issued guidelines in 1995 restricting its use in the UK to a maximum of six months.

Professor Gordon McVie, CRC director, said: "If there is a link between the treatments and a risk of ovarian cancer, or infertility and the disease, then we may be a step closer to understanding the causes of the disease.

"If researchers find there isn't a link, then it'll reassure thousands of women."

The scientists will compare the medical histories of 700 women who were given gonadotrophin fertility drugs to stimulate the ovaries with those of 2,000 women who had fertility problems but did not receive drug treatment.

Cancer takes many years

Fertility treatment may have serious side effects

Professor Allan Maclean, of the Royal Free and University College Medical School said: "We're having a look at a series of people who had fertililty treatment over a period of time.

"We will register those patients and see if there is an increased chance these women will develop cancer.

"We think it may take at least 10 years or maybe even longer (to develop cancer).

The peak period for women getting ovarian cancer is usually over the age of 50."

Conclusions from the study are not expected for several years.

If ovarian cancer is linked to infertility, and not its treatment, it would mean these women are more susceptible to cancer even before receiving treatment.

Professor Maclean said: "The consequences of that would be far-reaching and serious and it will be even more important that women get the proper support and advice."

"In recent years the number of infertility programmes has increased. If we find there's a relationship between treatments and an increased cancer risk, it will have major implications for those programmes.