For certain women, making some changes to their lifestyle may be all that's needed to boost their chances of getting pregnant after in vitro fertilization (IVF). A new international study suggests that women who smoke or who are obese face significantly lower odds of success with IVF.1 Their chances of having a live birth is also greatly reduced, the research found.
In younger women who smoke, their odds of IVF success are equivalent to those of women at least 10 years older, say the researchers from the Netherlands who published their study findings in the online version of the journal Human Reproduction April 7.
"In all subgroups, smokers had a lower delivery rate per treatment cycle than non-smokers," explained Bea Lintsen, MD, an obstetrician/gynecologist at University Nijmegen Medical Center in Zeist, The Netherlands, and this study's chief researcher.
The study was launched, Lintsen told Priority Healthcare, to examine IVF outcomes relative to specific infertility causes.
The harmful effects of smoking or obesity were the strongest for women with no apparent cause for their infertility, according to the study authors. "The positive news from our results, however, is that they suggest that couples—in particular, women with unexplained subfertility—may be able to improve the success of IVF treatment by quitting smoking and losing weight," Lintsen said.
The Link to Poorer IVF Outcomes
The research was a collaborative effort by doctors at a dozen medical institutions in the Netherlands who collected data from a percentage of patients involved in an unrelated hormone study. In all, records from more than 8,400 women were collected for the analysis. Information on their reproductive histories and lifestyle factors was examined, as well as medical records on the IVF treatment they had undergone from the early 1980s through 1995. Today, IVF is often combined with intracytoplasmic sperm injection (ICSI) in cases of male-factor infertility. However, since ICSI was not common during those years, the researchers did not evaluate the effect of that intervention.
Lintsen's team then divided the causes of the patients' infertility into four categories:
• Fallopian tube problems
• Male infertility
• Unexplained infertility
• Other causes (e.g. PCOS or endometriosis)
They analyzed IVF treatment outcomes for the first three causes.
The overall live birth rate per cycle was about 15%, according to the researchers. The birth rate was nearly 18% in couples with unexplained infertility, and women with tubal problems had about a 14.5% birth rate in the study. The lowest success rate was in cases in which male infertility was a factor: about 13.5%. The outcome of male factor infertility cases was poorer partly because ICSI was not used in the cases analyzed.
When Lintsen and her associates examined patient demographics, they found that about 40 percent of the women were smokers at the time they underwent their first IVF attempt, and more than 7 percent were overweight. (This was defined by collecting data on each woman's body mass index, or BMI, a measure of a person's healthy weight in relation to his or her height. People with a BMI of 25 to 29.9 are considered overweight, while individuals with a BMI of 30 or more are considered obese).2 Older women had lower success rates, regardless of their cause of their infertility. Their live birth rate dropped by 2% for each additional year of age.
Factors That Boosted Risk of Failure
When all the data had been analyzed, Lintsen's group found worse IVF outcomes for women who smoked or were overweight. "In all subgroups, smokers had a lower delivery rate per treatment cycle than non-smokers," Lintsen said. "The live birth rate for smokers was 28% lower than that of non-smokers." That's after taking other factors that could have affected IVF outcomes into account, such as age, body weight and duration of infertility, among others.
In women with no cause for their infertility, the detrimental impact of smoking was even more pronounced, accounting for a live birth rate of only 13% compared to 20% for non-smokers, the study authors learned.
Women who smoked also faced a greater likelihood of having a miscarriage, they added.
"Smoking has a devastating impact," said Didi Braat, MD, PhD, a professor of Obstetrics and Gynecology at University Nijmegen Medical Center in Zeist, and one of the study's investigators. "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 non-smoker in reproductive terms."
Further, overweight women faced worse IVF outcomes with a one-third lower chance of a live birth from their treatment cycle. As with smoking, the detrimental impact was worse in women with unexplained infertility. Only 14 percent of the obese women studied had successfully given birth compared to over 18 percent of the women of normal weight and nearly 21 percent of those who were slightly overweight, the researchers reported.
But the good news, Braat is quick to add, is that couples can boost their chances of success by undertaking lifestyle changes like quitting smoking and losing weight.
Few Theories Proposed
Why being obese and/or smoking has a negative impact on IVF isn't exactly known yet, Lintsen told Priority Healthcare. While she and her colleagues did not focus on why smoking is detrimental, they did cite a study published five years ago that suggested that smoking has genetic damaging effects on reproductive cells, negatively impacts the quantity and quality of eggs, and "leads to an early age of menopause."3
But the definitive answer remains elusive. "For these couples, we do know there's no problem with the fallopian tubes or with the sperm parameters," Lintsen said. "Causes could be found in the oocyte [egg] quality or endometrial receptivity."
The average older age of first-time mothers may partly explain this, as well, she said. As more and more women have their first child at an older age, the number of unexplained fertility cases is growing, she stated. "A low number of oocytes often also implies low quality of oocytes, and if fertilized, low quality of embryos," she said.
In women who are considered obese, changes in the receptivity of the uterus to a recently fertilized embryo may be partly to blame for the poorer IVF outcomes, as well as "disturbed endometrial function" caused by higher levels of estrogen that is more common in obese women.
What's Next?
Lintsen says she and her colleagues plan more studies in this regard. "We are doing a lot of research at this moment on couples with spontaneous pregnancies while waiting for IVF and prognostic factors that are involved with it," she said.
A study on the impact of stress on IVF outcome is also in the works. "For the moment, no other study is planned on smoking or overweight and IVF/ICSI," Lintsen said.
1. Lintsen MA, Pasker-de Jong PC, de Boer EJ et al. Effects of subfertility cause, smoking and body weight on the success rate of IVF. Hum Reprod 2005 Apr 7;[Epub ahead of print].
2. National Center for Chronic Disease Prevention and Health Promotion. Centers for Disease Control and Prevntion (CDC). Defining Overweight and Obesity. Available at: http://www.cdc.gov/nccdphp/dnpa/obesity/defining.htm#BMI. Accessed April 12, 2005.
3. Zenzes MT. Smoking and reproduction: gene damage to human gametes and embryos. Hum Reprod Update 2000 Mar-Apr;6(2):122-31.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
