Research has suggested that women who are stressed while trying for a baby are more likely to have girls.

A study has found that those who were under pressure at home, work or in their love life in the weeks or months before becoming pregnant had higher than usual odds of giving birth to a daughter rather than a son.

The finding, by Oxford University and U.S. researchers, means the economic downturn could see more women give birth to daughters. The study follows others that have shown the number of baby boys goes down following major upheavals.

For instance, in the months after the 9/11 terrorist attacks, the number of boys born in New York plunged, while the economic chaos that followed the collapse of the Berlin Wall saw far fewer boys born than expected in the former East Germany in 1991.

But the latest study is the first to link the phenomenon to the stresses and strains of everyday life and to rising levels of stress hormones.

Some 338 women from around the UK who were trying to get pregnant kept diaries about their lives and sex lives and filled in questionnaires about how stressed they felt. Levels of stress hormones including cortisol were measured in the months before pregnancy.

Of the babies born, 58 were boys and 72 were girls. Normally, in Britain 105 boys are born for every 100 girls.

When all the women were put together – stressed and calm – the result could have been due to chance.

But among the 50 per cent of the women who had the highest amounts of cortisol before pregnancy, the sex ratio was clearly skewed towards girls, the American Society for Reproductive Medicine’s annual conference heard.

The most stressed women were up to 75 per cent less likely to have boys than the least stressed, the conference in Orlando, Florida, was told. Cortisol levels rise when people suffer long-term stress such as pressure at work and bad relationships.

Money worries may also play a part, said Oxford University researcher Dr Cecilia Pyper.

It isn’t known why high levels of cortisol appear to cut the odds of having a boy. The gender of a baby is determined by the chromosomes in the father’s sperm and so is set at conception. But it is possible that high levels of cortisol somehow make it more difficult for male embryos to implant in the womb.

In addition, male babies may be more fragile and so more likely to be miscarried when cortisol levels are high, leading to more girls being born.

Dr Pyper and her co-researchers, from the U.S. government’s health research arm, only studied a small number of women and more work is needed to confirm the finding.