Stressed women are less likely to become pregnant, according to a new study published in a British medical journal. Experts suggest would-be mothers should try yoga or meditation to release stress.

The American study, published in the latest edition of Human Reproduction, involved 373 women between 18 and 40, whose stress levels were monitored at the start of a 12-month period when they attempted to get pregnant.

Researchers from Ohio State University measured two stress biomarkers in participants' saliva, the alpha-amylase and the cortisol. They found that, although there was no significant link between cortisol and how quickly a woman became pregnant, the relevance with alpha-amylase was obvious.

The highest one-third of the women in terms of salivary amylase were 29 per cent less likely to get pregnant each month. They were also more than twice as likely to be clinically infertile than the lowest one-third.

Dr Courtney Lynch, who lead the study, said: "For the first time, we've shown that this effect is potentially clinically meaningful, as it's associated with a greater than two-fold increased risk of infertility among these women."

She recommended that women having difficulty getting pregnant should consider stress-managing techniques, such as yoga and meditation. However, she also pointed out that stress is not the only factor involved in fertility problems and may only play a minor role.