Pregnant women exposed to large amounts of secondhand smoke - such as when their husband smokes - are more likely to miscarry during the first days of their pregnancy, new research shows.

“Women who are trying to become pregnant should be aware that passive smoking increases the risk of miscarriage,” study author Dr. Xiping Xu told Reuters Health.

Consequently, women trying to conceive should also try to avoid places where people are smoking, he said. And if their significant others smoke, they should stop, Xu added.

People are generally aware of the dangers of smoking, he said, but “it’s very good for the public to know that passive smoking is not good either.”

Xu, at Harvard School of Public Health, and his colleagues followed 526 nonsmoking women in China who were trying to conceive. The team performed highly sensitive urine tests every day, which alerted them to a pregnancy only days after it happened.

The researchers asked the participants’ husbands how much they smoked, and found that women whose husbands smoked at least 20 cigarettes each day were 80 percent more likely to miscarry within 6 weeks of their last periods than women whose husbands did not smoke.

Women whose husbands smoked less than 20 cigarettes per day showed a slightly higher risk of early miscarriage, as well.

Also, the wives of heavy smokers also appeared to take slightly longer to achieve a pregnancy that lasted at least 6 weeks than the wives of light or non-smokers, the authors report in the American Journal of Epidemiology.

In an interview, Xu noted that some of the miscarriages occurred very early in a woman’s pregnancy. Under normal circumstances, these women may have not even realized they were pregnant, thinking that the heavy bleeding accompanying the miscarriage was simply their period, he said.

Xu added that smoking may influence miscarriage risk by exerting a toxic effect on the pregnancy itself, or by disrupting the levels of crucial hormones.

“To maintain a pregnancy, you need appropriate hormone levels, and also you need a balance between all kinds of hormones,” Xu said.

SOURCE: American Journal of Epidemiology, May 15, 2004.