As if the dire warnings on cigarette packs weren't enough, pregnant women may have yet another reason to avoid tobacco.

A new study suggests smoking during pregnancy could reduce the fertility of baby boys when they grow up.

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The adult sons of women who smoked during pregnancy were more likely to have lower sperm counts and smaller testes than other men, Danish researchers found.

The sperm counts and other measures of fertility were still within normal ranges. However, the diminished levels are worrisome, says study co-author Dr. Tina Kold Jensen, a reproduction researcher based in Copenhagen.

Smoking is dangerous not only to the infant but also carries a risk into adulthood, she says.

Maternal smoking linked to many ills
Maternal smoking has been linked to a variety of health problems. Babies of mothers who smoke are more likely to have smaller lungs and develop asthma, says Dr. Norman H. Edelman, consultant for scientific affairs with the American Lung Association. Studies also have linked maternal smoking to other ills in children, including birth defects, colic, diabetes, mental retardation and obesity, along with premature labor for the mothers.

Scientists suspect adult males who smoke may suffer from fertility problems. But there's been little research into how smoking by pregnant women can influence the reproductive health of their children.

From 1995 to 1999, Jensen and colleagues enrolled young male military recruits from five European countries for a study of male reproductive health. More than 1,700 men volunteered from Denmark, Estonia, Finland, Lithuania and Norway.

The findings appear in the Jan. 1 issue of the American Journal of Epidemiology.

Sperm counts a quarter lower
The sperm counts of the men whose mothers had smoked during pregnancy were 24.5 percent lower than the other men. (Sperm counts refer to the amount of sperm in a single ejaculation.) Although the number of sperm in each millimeter of semen was less among the men of mothers who smoked- 41 million - it was still within the normal range, Jensen says.

The researchers also found the men's testes - the glands inside their testicles - were smaller, a factor that could contribute to the lower sperm counts, Jensen says.

Edelman says the study was well done, and its findings are very dramatic.

I'd love to see follow-up studies to determine if maternal smoking lowers testosterone levels as well, he says. If that turns out to be true, you're reducing not only fertility but masculinity. It opens up an incredibly interesting area of study.

Read more:
Commit to quit smoking
Smoking moms take big risk

 

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