A review of studies by Prof Richard Sharpe of the Queen's Medical Research Institute in Edinburgh has suggested that obese women and those who smoke during pregnancy can cause low sperm count in their sons.
"The high prevalence of low sperm counts in young men across Europe today is a cause for concern, especially when considered together with the trend for ever-later age for first pregnancy in the female partner," the review said.
It suggested that changes that take place when the baby is in the womb have a direct influence on sperm production in future life. Women who smoke or are heavily overweight during pregnancy pass on the risks to their sons and affect sperm production and sperm count.
The details of the review appear in a special issue of the journal Philosophical Transactions of the Royal Society B.