Stress factor can affect pregnancy
WOMEN who are stressed out while trying for a baby could be more likely to have girls, research suggests.
In the first study of its kind, experts found that high levels of the stress hormone cortisol were associated with the birth of more girls than boys.
Some 338 women in the UK who were trying to get pregnant kept diaries about their lives, relationships and sex lives, and completed questionnaires about how stressed they felt.
Levels of cortisol and the enzyme alpha-amylase (an indicator of adrenaline) were also measured on day six of the women's monthly cycle for a period of up to six months, or until they fell pregnant.
Cortisol is linked to longer-term chronic stress caused by ill health, a demanding job or money worries. Adrenaline, called the "fight or flight" hormone, is linked to short-term stress.
During the study, 61% (207 women) became pregnant.
Of the babies born, 58 were boys and 72 were girls, indicative of a "strong female excess", the researchers said.
The difference in the sexes was not significant overall, but was significant in the 50% of women with the highest levels of cortisol.
The research showed they were up to 75% less likely to have a boy.
No link was found with alpha-amylase.
Dr Cecilia Pyper, from the Department of Public Health at Oxford University, who worked on the study, said: "Chronic stress can be related to different stressful situations including financial pressures, stress at work, difficult relationships and problems related to physical or mental health.
"Long-term stress in women may be related to stress in the workplace or stress in the home, or to the long-term emotional stress of relationship difficulties.
"It is being recognised that long-term stress may be caused by financial difficulties.
"Women get stressed when they haven't got enough money to care for their families.
"They worry on a day-to-day basis about how they will find the next bit of money to pay the bills."
Previous research by the team, which includes experts from the National Institutes of Health in the US, found stressed women were less likely to fall pregnant during their fertile time than those who were calm.
Other studies have revealed that stressful disasters (either natural or man-made) can upset the gender ratio.
It is unclear why women with the highest levels of cortisol before pregnancy were more likely to have girls than boys.
The experts say more research is needed to see if the link between stress and sex ratio is genuine.
It is known that anxiety and stress in pregnant women may cause problems with the baby's development.
"Women trying to conceive are told how important it is for their future baby to take folic acid tablets, to stop smoking and to check they are immune to rubella," Dr Pyper said.
"If the findings are confirmed by larger studies, women may also be advised about reducing stress."