Men whose mothers smoked during pregnancy are more likely to need infertility treatment, researchers have said.
Previous research had suggested a link between smoking during pregnancy and infertility in male offspring, but scientists have now found the genetic basis for such an association.
According to experts at Aberdeen University, pregnancy smoking leads to significant reductions in the levels of a gene called DHH, which releases a molecule that helps to control normal testicle growth.
Dr Allan Pacey, secretary of the British Fertility Society, told the BBC that male fertility is often determined by what happens in the womb.
"Previous research has shown beef and pesticides in drinking water can have an impact on fertility," he revealed.
"We already know smoking is not advised during pregnancy and this helps us to understand why it affects fertility."
Infertility affects at least a fifth of couples of reproductive age and around 30 per cent of men are estimated to be sub-fertile.