The most common cause of female infertility may be caused by a hormonal imbalance before birth.
The findings, published this week in the New Scientist, reveal that polycystic ovary syndrome may be triggered before birth by excess exposure in the womb to a hormone called anti-Müllerian.
The condition affects up to one in five women worldwide - three-quarters of whom struggle to become pregnant.
The condition is typically characterised by high levels of testosterone, ovarian cysts, irregular menstrual cycles, and problems regulating sugar, but the causes have long been a mystery.
Robert Norman at the University of Adelaide said it is by far the most common hormonal condition affecting women of reproductive age but it has not received a lot of attention.
Paolo Giacobini at the French National Institute of Health and Medical Research and his colleagues found that the syndrome may be triggered before birth by excess exposure in the womb to the anti-Müllerian hormone.
They found that pregnant women with the syndrome have 30 per cent higher levels of this hormone than normal, and since the syndrome is known to run in families, they wondered if this hormonal imbalance in pregnancy might induce the same condition in the daughters of women with the condition.
It might also be why women with the condition seem to get pregnant more easily in their late 30s and early 40s.
Mr Norman said anti-Müllerian hormone levels are known to decline with age, usually signalling reduced fertility. But in women who start out with high levels, age-related declines may bring them into the normal fertility range - although this still needs to be tested.
A drug trial is set to begin later this year.