The study appears in the May issue of the journal Human Reproduction.

Researchers say the effect is so clear they are already warning their patients to avoid exposure to secondhand smoke.

"Our data demonstrate that the effects of [ secondhand smoke ] are equally as damaging as [firsthand] smoke on fertility," Michael Neal, PhD, and colleagues write.

May 25, 2005 -- It's known that smoking can affect a women's fertility , but now a study shows living with a smoker is as damaging as being a smoker.

Smoke Affects Fertility

In the study, 225 women undergoing infertility treatments were asked whether they were nonsmokers, smokers, or living with a partner who smoked regularly. The researchers then compared success rates of the fertility treatments for the three groups.

The women had undergone either in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI), an enhanced form of IVF in which a single sperm is injected into the egg.

"Despite similar embryo quality there was a striking difference in implantation and pregnancy rates," they write.

Per embryo transferred:

48% of nonsmokers became pregnant

19% of smokers became pregnant

20% of women living with a smoker became pregnant

The authors note that the study was limited by its reliance on self-reported exposure to secondhand smoke. Although the findings are important, these results will need to be confirmed in another study with more objective measures of cigarette smoke exposure, such as looking at a dose-related effect on fertility, they write.

Despite the need for further study, the researchers say they are already advising patients about the impact of secondhand smoke on fertility. According to researcher Warren Foster, "the findings from our study already warrant a warning to women to reduce or, if possible, prevent exposure to cigarette smoking, especially if they are trying to conceive."