This might have a message for the need for quite high levels of physical activity during pregnancy

Professor Jane Wardle, Cancer Research UK

Each 2.2lbs increase in weight raises the breast cancer risk by about 4% when adjusted for weight and height before pregnancy.

Pregnancy weight gain has been linked in previous studies to increased oestrogen levels, which in turn are believed to increase breast cancer risk.

UK cancer experts say it corroborates research which shows the link between obesity and an increased risk of breast cancer.

Study investigator Dr Leena Hilakivi-Clarke said: "Significant weight gain during pregnancy may cause changes in breast tissue that increase susceptibility to breast cancer in later life - roughly equivalent to the risk of postmenopausal obesity.

"Women who retain the added pounds after pregnancy are at the greatest risk."

Preventive measures

Weight gain during pregnancy appeared to increase breast cancer risk only after menopause, said Dr Hilakivi-Clarke.

Weight gain of 25 to 35 pounds is normal in pregnancy and not associated with an increase in risk for either premenopausal or postmenopausal breast cancer, the study found.

The findings were presented at the American Association for Cancer Research (AACR) annual meeting in San Francisco.

Professor Jane Wardle, director of Cancer Research UK's health behaviour unit, said there was a growing body of evidence linking obesity with post menopausal breast cancer.

She said: "This might have a message for the need for quite high levels of physical activity during pregnancy.

"Maybe we need to pay more attention to women's lifestyles during pregnancy.

"Nobody is really sure what the mechanism is for the breast cancer and obesity link, but it's widely believed to be very important now."

In Europe, about half the adult population is currently overweight, and urban areas of many developing countries have a similar prevalence, according to the International Agency for Research on Cancer.

Scientists have estimated that in the European Union, 21,000 cases of colon cancer and 13,000 cases of breast cancer could be avoided annually by people maintaining a normal body weight.