Stressed-out women are 12pc less likely to fall pregnant than those who are calm, experts said today.
While women have long been told to relax when trying for a baby, the evidence behind such claims has largely been anecdotal. Now, scientists have shown the importance of relaxation when it comes to falling pregnant.
They carried out saliva tests on 274 women and analysed levels of the stress hormone cortisol and the enzyme alpha-amylase (an indicator of adrenalin levels).
All the women were aged between 18 and 40 and were trying for a baby naturally.
The women had been trying for three cycles or fewer prior to the start of the study and had not undergone fertility treatment.
The researchers from Oxford University carried out the tests on day six of each woman's menstrual cycle, using fertility monitors to identify ovulation, for a total of six cycles or until the woman fell pregnant.
The study, published in the journal Fertility and Sterility, found no effect from cortisol on the chances of falling pregnant.
But women in the group with the highest levels of alpha-amylase had a 12pc lower chance of falling pregnant for each day of their most fertile days than those with the lowest levels.
The authors concluded: "Stress significantly reduced the probability of conception each day during the fertile window."
Dr Cecilia Pyper, from the National Perinatal Epidemiology Unit at the Oxford University, said: "This is the first study to find that a biological measure of stress is associated with a woman's chances of becoming pregnant that month.
"The findings support the idea that couples should aim to stay as relaxed as they can about trying for a baby.
"In some people's cases, it might be relevant to look at relaxation techniques, counselling and even approaches like yoga and meditation."