In an article published in the journal Human Reproduction, researchers have reported that exposure to cigarette smoke in mice while before, during and after pregnancy reduced fertility through impaired development of the testes, and lowered sperm counts.

Dr Allan Pacey, Senior Lecturer in Andrology, University of Sheffield, said:

“We have suspected for some time that one of the most important times for a man’s fertility is during the period before he is born and when he is still inside his mother’s womb or during those early weeks when he is being breast-fed and absorbing his mother’s breast-milk. We think this is because, during this time, the testicle is at its most sensitive and the population of testicular stem cells, which go on to produce sperm after puberty, is established. So any external factors the boy is exposed to through his mother’s blood supply or through breast milk has the potential to upset this process and decrease his fertility later in life.

“We have long suspected that maternal smoking during pregnancy could be one of those factors detrimental to her son’s future fertility. In 2007 an intriguing paper was published in the American Journal of Epidemiology suggesting that the semen quality of the sons of women who smoked during pregnancy was lower than that from the sons of non-smokers. This supported the hypothesis that exposing the baby’s testicles to toxins during pregnancy could affect his adult fertility many years later. But it has been very difficult for scientists to do any further work in the human because of obvious ethical and technical difficulties of working with human subjects.

“Therefore, the paper by Professor McLaughlin is a very welcome study which not only confirms the hypothesis that exposure of boys in utero to compounds in cigarette smoke is detrimental to adult testicular function; but it also goes some way to establish the mechanism by which this may be achieved. It is very elegantly designed and the authors should be commended. This study should send an important signal to couples about the dangers that smoking during pregnancy has on the future reproductive health of their infant. Health professionals should advise couples of the dangers and should make an appropriate referral to a ‘Smoking Cessation Service’ if the couple need help to stop smoking.

Prof Sheena Lewis, Professor of Reproductive Medicine at Queens University Belfast and Chair of British Andrology Society, said:
“This is a well-designed and carefully executed study. It was performed in an animal model as such mechanistic experiments are impossible and unethical in humans. However, the results are very clear. Mums who smoke when pregnant are potentially doing irreversible damage to their sons’ fertility. If these Mums care about their sons’ future happiness and want grandchildren, they should stop smoking during pregnancy.”

Mr Stuart Lavery, Consultant Gynaecologist, Director IVF Hammersmith, Hammersmith Hospital, said:
“We have known for many years that women who smoke during pregnancy put their babies at higher risk of adverse outcomes. There has been increasing evidence to show that these risks can carry longterm consequences for their children. This well designed experiment conducted in mice has shown a reduction in the sperm parameters and fertility of the male offspring. As the researchers point out it would be unethical to repeat this experiment in humans however it brings additional evidence and weight to the advice that women should stop smoking not only for their own health benefit to but also to protect the longterm health and reproductive potential of their children”

“Damaging legacy: maternal cigarette smoking has long-term consequences for male offspring fertility” by A.P. Sobinoff et al. published in Human Reproduction on Wednesday 1st October.