Smoking mothers may leave their sons infertile

Scientists found numbers of immature reproductive cells were dramatically reduced by 41 per cent in male embryos exposed to the effects of tobacco.

The findings echo those of previous research showing a similar effect on female embryos and were published alongside the results of a second study explaining why men who smoke may be putting their fertility at risk.

Experts say the studies may explain an increasing trend towards reduced fertility and reinforces public health advice urging couples to quit before attempting to conceive.

The first team led by Professor Claus Andersen, from the University Hospital of Copenhagen in Denmark looked at 24 embryonic testes obtained from legally terminated pregnancies.

Each of the aborted male embryos was between 37 and 68 days old.

The scientists compared the number of germ cells – immature cells that become sperm in males and eggs in females – in the testes of embryos from smoking and non-smoking women.

Those from smokers contained less than half as many germ cells as those from non-smokers. The number of non-reproductive somatic cells was also reduced by more than a third in the testes of embryos from smoking mothers. The more a woman smoked the more impact it had.

Previous research looking at the effect of smoking on female embryos found a similar pattern, said the researchers writing in the journal Human Reproduction.

Overall, the number of germ cells in male and female embryos exposed to tobacco smoke were reduced by 41 per cent.

Professor Andersen said: "As the germ cells in embryos eventually develop to form sperm in males and eggs in females, it is possible that the negative effect on the numbers of germ cells caused by maternal smoking during pregnancy may influence the future fertility of offspring."

Prof Andersen stressed the first three months of pregnancy was a

crucial time when the developing embryo's sexual organs are differentiating to form either male testes or female ovaries.

Scientists still do not know whether the reduction in embryonic cell numbers is permanent, or reflects a growth delay that is compensated for later on.

The second study, also published in Human Reproduction, focused on levels of proteins called protamines that play an important role in the development of sperm.

A team led by Professor Mohamed Hammadeh, from the University of Saarland in Homburg Saar, Germany, looked at the levels of two protamines – P1 and P2 – in the sperm of 53 heavy smokers and 63 non-smokers.

It found that, compared with non-smokers, P2 concentrations were 14 per cent lower in the sperm of men smoking more than 20 cigarettes a day. In addition the relative levels of P1 and P2 were altered in smokers.

Prof Hammadeh said: "In normal fertile men, the ratio of P1 to P2 is almost equal at 1:1. Any increase or decrease in this ratio represents some kind of infertility."

He added: "Given the potential adverse effects of smoking on fertility, cancer and so on, physicians should advise infertile patients who smoke cigarettes to quit smoking."

Fertility expert Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield, said: "These two studies provide further proof that the smoking of cigarettes is bad for the reproductive system of men and women.

"Clearly couples trying to conceive should not smoke and should avoid exposure to cigarette smoke. To make sure sperm are healthy, this needs to be sustained as it takes about three months to produce a cohort of sperm: stopping smoking on Friday does not mean healthy sperm by Monday."