THURSDAY, April 7, 2005 (HealthDayNews) -- Women who smoke or are overweight substantially reduce their chances of getting pregnant by in vitro fertilization (IVF), a new study finds.
In reproductive terms, the Dutch study found smoking adds 10 years to a woman's age, making it harder for her to conceive. For example, a 30-year-old woman who smokes has the same chance of getting pregnant by IVF as does a 40-year-old nonsmoker, according to the report published in the April issue of Human Reproduction.
"We studied more than 8,000 women who had IVF," said researcher Dr. Didi Braat, a professor of obstetrics and gynecology from the Academic Hospital Nijmegen St. Radboud, The Netherlands. "We found that the chance that you can become pregnant if you smoke is significantly lower than women who didn't smoke."
In their study, Braat's team collected data on 8,457 women who underwent IVF from 1983 to 1995. More than 40 percent smoked while undergoing their first attempt at IVF, and more than 7 percent were overweight.
The researchers found that, compared with women who didn't smoke, those who did were 28 percent less likely to conceive and deliver an infant. And compared with normal weight women, overweight women were 33 percent less likely to have a baby.
Among smokers, "we found that this lower chance of having a baby was comparable to an increase of 10 years in the women's age," Braat said. "Also, if you are pregnant, there is a larger chance to lose the baby if you smoke, compared to the women who don't smoke."
"We have always told women to stop smoking if they want to become pregnant, but now we have a large study to confirm to them that they should stop smoking," Braat said.
Braat admits that she doesn't know how long a woman should stop smoking to reduce the effects on the success of IVF. In addition, why smoking has this effect is also not known. Braat speculated the smoking might affect the lining of the uterus or the outer layer of the egg.
"Stop smoking immediately," Braat advised. "It increases your chances to become pregnant, so you might not need IVF. You have a better chance of having a baby, and less of a chance of having a miscarriage. It's also better for the baby. And also try to lose weight."
Dr. Owen K. Davis, co-director and an associate professor at the Center for Reproductive Medicine and Infertility at Weill Medical College of Cornell University, agreed that both smoking and being overweight are factors that negatively affect pregnancy.
"The finding about smoking is significant and is in accordance with the findings of other studies," Davis said. "Smoking does have toxic reproductive effects."
"Clearly, for the health of their pregnancy, as well as their overall long-term health and reproductive performance with IVF, they should be at an optimal body weight and they should quit smoking," Davis advised. In addition, "Smoking can accelerate the onset of menopause," he said.
Another expert, Dr. David F. Archer, a professor of obstetrics and gynecology and director of the CONRAD Clinical Research Center at Eastern Virginia Medical School, said, "I encourage women to stop smoking when they start considering they want to become pregnant."
The American Society for Reproductive Medicine can tell you more about in vitro fertilization.