Smoking while pregnant could reduce the fertility of baby boys by affecting a key testis gene, according to a University of Aberdeen led study.
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. However in a paper that appears online in the Journal of Clinical Endocrinology and Metabolism they provide new insights into how this may occur.
It is already known that pregnant women who continue smoking have a higher risk of giving birth to pre-term birth, underweight babies. Such babies also have an increased risk of a wide range of problems, including asthma, developmental abnormalities of the face and behavioural and educational difficulties.
Now researchers have made a new finding that cigarette smoke can affect a key testis gene called DHH. This gene causes the DHH molecule to be released by certain testis cells as a signal to tell other cells what to do and is important in controlling development of the normal testicle.
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."
Professor Siladitya Bhattacharya, Professor of Reproductive Medicine and Head of Obstetrics and Gynaecology at the University of Aberdeen, added: "These findings reinforce the very clear message to women that they should not smoke during pregnancy."
The researchers say cigarette smoke is very complex, consisting of a cocktail of chemicals including a large family of toxic ones called PAHs.
PAHs are known to reduce fertility in adults and in this study they were found to be present at surprisingly high concentrations in the fetal liver. However, the team do not yet understand exactly how PAHs and other chemicals affect the developing fetus in the womb.
Dr Fowler added: "We suggest that exposure of the developing fetus to small changes in levels of a complex mixture of chemicals, such as those in cigarette smoke, can damage the development of their testicles and result in reduced fertility."