IVF treatment increases the risk of going on to develop breast cancer, a new study suggests.

Data from more than 626,000 women over 21 years found links indicating that women over 40 who undergo the treatment are 65 per cent more likely to develop the disease.

The increased risk across all ages was 10 per cent.

In preparation for IVF, women are given drugs to stimulate the ovaries into producing more eggs.

This also means increased levels of oestrogen in the body, which scientists believe may explain the cancer link.

A team at Copenhagen University tracked 59,000 women who gave birth after undergoing fertility treatment, then compared them with 567,000 women of equal age who had a child naturally.

Over the study period 3,894, or less than 1 per cent, of the women were diagnosed with breast cancer.

Professor Geeta Nargund, from St George’s Hospital, London, said: “This is a finding of great significance.

“Women are more prone to breast cancer as they get older, particularly if they have never given birth to a child.

“On top of that if you add stimulation drugs which increase oestrogen levels, this risk further appears to be increased.

She added: “This is a wake-up call about the use of high dose stimulation in IVF, especially in women over the age of 40.