Women who are stressed during pregnancy have a higher than usual chance of having a baby girl, scientists from Oxford University and the US government's health research arm have claimed.

In a detailed study of 338 women from around the UK, the researchers looked at the influence of the stress hormone cortisol on the pregnancy and births. They found that in the women who had the highest levels of the hormone, the figures for them giving birth to a baby girl were heavily skewed. They found that the most stress women were up to 75 per cent less likely to have a boy than the least stressed.

The findings present something of a challenge for the researchers, as the gender of the baby is determined by chromosomes in the father's sperm. The researchers believe the levels of stress hormone could make it harder for male embryos to implant in the womb.

As a result, the scientists have said more research is needed into the area.