Fertility treatment does not increase a woman's risk of developing breast cancer, according to a study of more than 25,000 women in the Netherlands.

The large study will help to reassure patients concerned that the powerful hormone doses that are part of fertility treatment might put them at risk of developing the disease in the future.

At the beginning of an IVF treatment cycle, women are given hormone drugs to stimulate their ovaries to produce more eggs so that clinicians can produce fertilised embryos in vitro. These lead to large spikes in oestrogen levels that could promote the development of breast cancer, which is sensitive to the hormone.

The study, carried out by Dr Alexandra van den Belt-Dusebout at the Netherlands Cancer Institute in Amsterdam, compared 18,970 women who had had at least one cycle of IVF treatment with 7,536 women who had not received fertility treatment between 1980 and 1995. They matched these patients to records in the National Cancer Registry.

Of the 378 women who developed breast cancer, 266 were in the IVF group and 112 were in the non-IVF group. After adjusting for known risk factors such as age, the number of children the women had and family history of breast cancer, the team found no statistical difference between the two groups, showing that IVF treatment does not increase a woman's chances of developing breast cancer.

Van den Belt-Dusebout presented her results at the American Society for Reproductive Medicine in San Francisco.

"From 10 years after treatment, breast cancer risk was moderately increased in the IVF group but also in the non-IVF group, compared to the general population," the researchers said.

Meanwhile, two new studies have revealed that women who receive acupuncture at the same time as IVF treatment are no more likely to have a baby.

Both were randomised placebo-controlled trials in which the effect of acupuncture was compared with a sham procedure. Neither the patients nor the clinician evaluating their pregnancy knew who had received the true treatment.

Acupuncture aimed at improving IVF success rates is widely offered by fertility clinics in the UK. In the first of the studies, researchers in Hong Kong split 370 women receiving IVF into two groups. One group received real acupuncture before and after having an IVF embryo implanted into their uterus. The other had the same procedure, except the treatment used retractable needles that did not penetrate the skin.

Of the 185 who received the sham treatment, 91 achieved a clinical pregnancy (foetal heartbeat identified using ultrasound) and 71 had a successful delivery. This compared with 72 clinical pregnancies in the true acupuncture group and 55 live births. The differences between the groups were not statistically significant.

Dr Ernest Ng, in the department of obstetrics and gynaecology at the University of Hong Kong, said that his methodology was the most powerful way of evaluating whether acupuncture was effective. His results are published in the journal Human Reproduction.

In a second study, researchers in Chicago used a similar design in which 124 women received true or sham acupuncture. The control group had their skin punctured by real acupuncture needles, but not at genuine "Qi-lines" on the body.

In the true acupuncture group, 43.9% achieved a clinical pregnancy, compared with 55.2% of the women given the sham treatment. The results were presented at the American Society for Reproductive Medicine's annual meeting in San Francisco yesterday.