The use of some alternative medicines might interfere with infertility treatment, a major conference on reproductive science has been told.

Welsh researchers found that women who used herbal medicines, acupuncture and reflexology while undergoing IVF (in vitro fertilisation) were nearly a third less likely to become pregnant.

A team led by Jacky Boivin, a psychologist at Cardiff University, studied 818 women who wanted to conceive for a year. There were 261 women who tried alternative therapies in the hope they would reduce stress and enhance the IVF process. Many were taking nutritional supplements.

But the results for this group were that they were 30% less likely to become pregnant.

The Cardiff team believes some herbal remedies could interfere with the action of drugs taken to promote IVF.

Stress however is also a big factor. Many of the women who turned to alternative therapies had been trying to get pregnant for some time and were very anxious about the outcome.

Dr Boivin said repeated failure with fertility treatment might cause women to seek unconventional help.

"But it may be that complementary therapies diminish the effectiveness of medical interventions," she said. "For example, it could be that there are interactions between herbal medicines and fertility medicines."

"Perhaps women should hold off until they have tried conventional fertility treatments."

Edzard Ernst, professor of complementary medicine at Exeter University, said: "Those women who are more prone to stress and have more health problems are more likely to try complementary medicine, so complementary medicine could only be a marker, and not the cause, of stress or lower success rates."

No chemical evidence was included in the study, which was presented to the European Society of Human Reproduction and Embryology meeting in Lyon, France.