NEW YORK (Reuters Health) - Women who were exposed to their parents' smoking as children may have a higher likelihood of suffering a miscarriage, new research suggests.

In a study of nearly 2,200 non-smoking pregnant women, researchers found that those exposed to their parents' secondhand smoke during childhood were 80 percent more likely to have a miscarriage compared with women whose parents didn't smoke.

The findings appear in the American Journal of Epidemiology.

It's known that parents' smoking can harm developing fetuses and children, contributing to early-life problems like low birth weights and asthma. But this is the first study to show a link between childhood exposure to parents' smoking and reproductive ability in adulthood, according to lead author Dr. John Meeker, University of Michigan School of Public Health, and associates.

More research is needed to confirm the finding, Meeker, an assistant professor of environmental health sciences, told Reuters Health. However, he added, the results fit in with the body of research showing that early-life exposure to environmental stressors -- including tobacco smoke -- may have health effects that manifest in adulthood.

The findings are based on pregnancy outcomes of 2,162 women who underwent assisted reproduction treatments at one of three Boston fertility clinics.

The researchers found that a woman's risk of miscarriage tended to go up in relation to parents' smoking, being highest among those exposed to secondhand smoke from both parents.

It's not fully clear why childhood exposure to tobacco smoke would affect a woman's miscarriage risk. However, Meeker and his colleagues point out that tobacco smoke contains thousands of chemicals, including some that are known or thought to harm reproductive health -- such as lead, benzene and cadmium.

The developing reproductive system in children may be particularly vulnerable to such exposures.

"It is known that childhood is a developmentally sensitive period during which the body is susceptible to adverse effects from hazardous exposures," Meeker explained.

"Children of smokers can experience very high levels of secondhand smoke exposure at home, in the family car, and in other locations."

There is "more than enough" evidence from medical studies to tell us that children need to be shielded from secondhand smoke, according to Meeker.

"Our results," he said, "suggest that we should prevent these exposures not only for the health of our children, but perhaps our grandchildren as well."

SOURCE: American Journal of Epidemiology, September 1, 2007.