It has been known for some time that smoking can affect a woman's fertility, but Canadian research published (Thursday 26 May) in Europe's leading reproductive medicine journal Human Reproduction suggests that exposure to side-stream smoking – smoke given off by a smouldering cigarette - is just as damaging.
In a study of women undergoing IVF or ICSI, researchers from McMaster University and Hamilton Health Sciences, in Hamilton, Ontario, examined the quality of embryos and the implantation and pregnancy rates of 225 women who were grouped according to whether they were non-smokers, smokers or side-stream smokers – side-stream smokers being defined as women who lived with a partner who regularly smoked.
They found no difference in the quality of the embryos from the three groups. But, there was a striking difference in implantation and pregnancy rates between the non-smoking group and the smokers and side-stream smokers.
The risk of side-stream smoking on reproductive health was unknown until now, but the evidence from this study of the damaging effect is so clear that the researchers are now warning all their patients of the potential hazards, according to lead researcher Michael Neal, PhD candidate at McMaster University and Hamilton Health Sciences.
"We found that embryo quality and fertilisation rates were similar in the three groups, but there was a significant difference in the pregnancy rates per embryo transfer with the non-smokers achieving around 48%, the smokers around 19% and the side-stream smokers 20%. When it came to implantation rates, which we calculated as the number of foetal sacs with a positive heartbeat divided by the total number of embryos transferred, we found that while non-smokers achieved a 25% implantation rate, both smokers and side-stream smokers managed only around 12%."
Senior researcher Professor Warren Foster, director of IVF and reproductive biology at the Centre for Reproductive Care at McMaster University's Department of Obstetrics and Gynecology, said that this was a retrospective study relying on self-reported smoking habits and should be confirmed by a prospective study with objective measures of cigarette smoke exposure, which would also test for possible dose-related effects, though none were identified in this study.
"Although we do need a prospective confirmatory study, 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," he said.
The researchers plan to undertake a prospective study if funding for a research proposal under review is forthcoming. They are also looking for possible collaborators.
Meanwhile, they are trying to establish why there was no difference in the appearance and development of the pre-implantation embryos from all three groups, yet a significant decrease in the ability of the embryos from smokers and side-stream smokers to implant and/or maintain a pregnancy.
"This was the most striking finding from our study," said Mr Neal.
It was possible, he said, that cigarette smoke compromised the competence of the egg, perhaps by disrupting the proliferation of the granulosa cells in the egg follicle and their production of the oestrogen-producing enzyme aromatase, but that the lethal results were not apparent until later in embryonic development. However, this was still only speculation.
It was clear, the researchers concluded, that it is essential to study the effects of cigarette smoke on the female gamete. The damaging effects on sperm are well documented as sperm are more accessible and easier to study. Studying the female gamete, on the other hand, is much more difficult since human ooctyes are precious.
"Our study is unique in looking at the female, who is just as vulnerable, if not more vulnerable to environmental toxicants such as cigarette smoke," said Mr Neal. "An isolated follicle culture system that we have developed is now allowing us to investigate the effects of smoking contaminants on follicle growth in vitro and this will give us the chance to address some of the questions that would otherwise be difficult to answer."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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