Women who take oral contraceptives run a higher risk of developing cervical cancer, but this risk is transient and reverts to normal about 10 years after they stop, British researchers said on Thursday.

Other studies have found a link between taking the pill and cervical cancer, but this is the first to show how long this risk persists, according to the study in the journal Lancet. Dr. Jane Green, a cancer epidemiologist from Britain's University of Oxford, studied data from 24 studies involving more than 16,000 women with cervical cancer and more than 35,000 without.

For women in developed countries who took the pill from age 20 to 30, the number of cases of cervical cancer by age 50 rises to 4.5 per 1,000 women, from 3.8 cases per 1,000 in women who did not take the pill.

The incidence rises to 8.3 cases per 1,000 for pill users in less developed countries, compared with 7.3 cases per 1,000 for women who did not take the pill.

But this extra risk is outweighed by a reduction in the risk of ovarian and endometrial cancers, the researchers said in a statement.

Cancer researcher Ciaran Woodman of the University of Birmingham said the study reinforces the need for routine screening for cervical cancer.

"The take-home message should be that all women must come for screening when invited," she said in a statement.

Cervical cancer is the second most common type in women and the leading cause of cancer death in some countries. Virtually all cases of cervical cancer are caused by the sexually transmitted human papillomavirus or HPV.