Having a baby slashes a woman’s risk of developing ovarian cancer by up to 40 per cent, a study has found.

The likelihood goes down by a further 8 per cent for every additional child she has afterwards, Oxford academics discovered.

They suspect the link is due to the female hormone oestrogen, which is known to trigger tumours and is significantly lowered during pregnancy.

Life saver: Having a baby slashes a woman’s risk of developing ovarian cancer by up to 40 per cent, a study has found (file image)

In a study of 8,000 women aged 50 and above, the experts found that having at least one child reduced a woman’s average risk of ovarian cancer by 20 per cent. But it was cut to 40 per cent for two particular types of the disease – endometrioid and clear cell tumours.

These are rarer forms of the illness that affect less than a tenth of the 7,000 women diagnosed with ovarian cancer in the UK each year.

Ovarian cancer is referred to as the ‘silent killer’ as the early symptoms are often confused with irritable bowel syndrome, period pain or the menopause. For this reason, tumours are commonly detected too late to be treated. The disease kills around 4,200 women a year.

The study, to be presented today at the National Cancer Research Institute conference in Liverpool, is one of the first to look at the extent to which childbirth prevents the different tumours.

Professor Charlie Swanton, chair of the NCRI Cancer Conference, said: ‘We’ve known for some time that the number of children a woman has, and her use of contraception, can influence her risk of ovarian cancer, so this research provides important further detail about different types of the disease.

‘Ovarian cancer – like many other cancers – is not one disease but different diseases that are grouped together because of where they start.

Ovarian cancer is referred to as the ‘silent killer’ as the early symptoms are often confused with irritable bowel syndrome, period pain or the menopause (file image)

‘It’s important to know what affects the risk of different types of ovarian cancer and what factors impact this.

‘We now need to understand the mechanisms behind these findings to develop some way to extend this lower risk to all women, regardless of how many children they have.’ Previous research has shown that breastfeeding and taking the contraceptive pill reduce the risk of ovarian cancer, as both also suppress oestrogen.

This research could help us to develop new, more effective, treatments for ovarian cancer. Annwen Jones, chief executive of the charity Target Ovarian Cancer

Lead researcher Kezia Gaitskell, of Oxford University’s Cancer Epidemiology Unit, said infertility may also be linked to the disease.

One reason women struggle to conceive is that they are suffering from endometriosis, a painful condition of the womb which is also thought to increase the risk of cancer.

Dr Gaitskell said: ‘We think that the significant reduction in risk among women with one child compared to women without children is likely to be related to infertility.

‘There are some conditions, such as endometriosis, that may make it harder for a woman to become pregnant, and which may also increase her risk of these specific types of ovarian cancer.’

Annwen Jones, chief executive of the charity Target Ovarian Cancer, said: ‘This research could help us to develop new, more effective, treatments for ovarian cancer.