In a study of women undergoing IVF or ICSI[3], 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[4] – 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."
[1] Side-stream smoking is equally as damaging as mainstream smoking on IVF outcomes. Human Reproduction. doi:10.1093/humrep/dei080.
[2] Side-stream smoking is strictly defined as smoke that is emitted from the smouldering end of the cigarette and contains the most toxic constituents. Passive smoke includes side-stream smoke along with smoke exhaled by the smoker.
[3] IVF = in vitro fertilisation. ICSI = intracytoplasmic sperm injection: process by which an egg is fertilised by injecting a single sperm into the egg.
[4] The 39 smokers in the study smoked a mean of 11 cigarettes a day. Their partners smoked a mean of 10.7 a day (8 were non-smokers). Of the 40 side-stream smokers, the male partners smoked a mean of 10.8 cigarettes a day. 146 women were non-smokers (i.e. neither they nor their partners smoked).
Notes:
1 PDF version of this press release and full embargoed text of the paper with complete results can be found from 09:00hrs London time Tuesday 24 May at: http://www3.oup.co.uk/eshre/press-release/may052.pdf or is available from Margaret Willson.
2 Human Reproduction is a monthly journal of the European Society of Human Reproduction and Embryology (ESHRE). Dr Helen Beard, Managing Editor. Tel: +44 (0) 1954 212404 Email: beardh@humanreproduction.co.uk
Please acknowledge Human Reproduction as a source.
3 ESHRE's website is: http://www.eshre.com
4 Abstracts of other papers in ESHRE's three journals: Human Reproduction, Molecular Human Reproduction & Human Reproduction Update can be accessed post embargo from http://www3.oup.co.uk/eshre/ Full text of papers available on request from Margaret Willson.
Journal
Human Reproduction