"Both smoking and being overweight unfavorably affect the live birth rate after IVF," says researcher Didi Braat in a news release.
Her message is clear: Ditch the cigarettes and excess weight, especially for women with unexplained infertility.
"This group in particular may be able to improve the outcome of subfertility treatment by quitting smoking and losing weight," says Braat, a professor of obstetrics and gynecology at Radboud University in the Netherlands.
Even a few extra pounds could make a difference. Disappointing IVF results weren't limited to obese women, says the study, which appears in the online edition of Human Reproduction.
Smoking Hinders IVF Success
"Smoking has a devastating impact," says Braat. "It is comparable to adding a decade to the reproductive age of a 20-year-old. This means it makes her the equivalent of a 30-year-old nonsmoker, in reproductive terms."
The finding is based on more than 8,400 women in the Netherlands who tried IVF from 1983-1995. All Dutch IVF clinics participated.
Of all the women in the study, 43% smoked during their first in vitro fertilization attempt. For every type of fertility problem, the delivery rate was higher for women who didn't smoke.
Smoking slashed the live birth rate by 7.3% among women with unexplained infertility. Even though women who smoked received slightly more embryos per cycle with IVF, they still had lower pregnancy rates and were more likely to miscarry.
Another Drawback: Excess Weight
A woman's weight also affected her chances of in vitro fertilization success.
Those with a normal or slightly overweight BMI (body mass index) had a significantly higher live birth rate per IVF cycle than those who were overweight. The rate for underweight women was similar to those with normal BMI, say researchers.
Keep in mind that those categories fall short of obesity. Normal BMI ranges from 18.5 to 24.9. Overweight BMI runs from 25-29.9, and obesity is a BMI of 30 or higher.
What does that mean in the real world?
Let's say you're 5-feet-3-inches tall. If you weigh 140 pounds, your BMI is 25 -- the lower end of the overweight category. Add just 10 pounds, and your BMI hits 27. That's the beginning of the range that had fewer IVF live births in the study.
By the way, once the scale hits 170 pounds for a 5-foot-3-inch woman, her BMI is 30. That's considered obese.
In addition to infertility problems, obesity carries all kinds of health risks, including diabetes.
The data date back at least a decade. "Success rates in these older data might differ from the success rates today," the researchers write. But it can't hurt to be smoke-free and in your best possible shape.
"These results suggest that women, and in particular those with unexplained subfertility, may be able to improve the outcome of subfertility treatment by quitting smoking and losing weight," the researchers write.
SOURCES: Lintsen, A. Human Reproduction, online edition, April 7, 2005. WebMD: BMI Calculator. WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Weight Loss: Body Mass Index (BMI)." News release, Human Reproduction.
By Miranda Hitti
Reviewed by Charlotte E. Grayson, MD
© 2005, WebMD Inc. All rights reserved