The research led by the University of Aberdeen found evidence that smoking while pregnant affects a key testis gene called DHH, which is important in controlling development of the normal testicle.
Researchers say there is already evidence that there is a greater chance of boys developing abnormal penises and poorly descended or smaller testicles if their mothers smoked during pregnancy.
Normal human fetuses between 11 and 19 weeks of pregnancy were examined by the team who discovered a significant reduction in DHH if the mother smoked.
Dr Paul Fowler, Senior Lecturer in Reproductive Physiology at the University of Aberdeen, led the study which also involved the Macaulay Institute, Aberdeen, the University of Nottingham and the University of Glasgow.
He said, “This is the first time that the gene DHH, which plays a key role in the male’s normal development, has been linked to maternal smoking and fertility problems.
“Our research is still preliminary and a lot more work needs to be done, but what we did find suggests that lowered DHH may be a reason why baby boys of women who smoked ten or more cigarettes a day during pregnancy were at a higher risk of abnormalities and future fertility problems.”