Canadian researchers have discovered that a woman's fertility can be affected almost as much by passive smoking as by actual smoking. Published this week in the journal Human Reproduction, the study shows that exposure to 'side-stream smoking' - defined as smoke given off by a smouldering cigarette - is equally damaging to women undergoing fertility treatment.
The researchers, from McMaster University and Hamilton Health Sciences in Ontario, studied the quality of embryos produced by 225 women undergoing IVF or ICSI. The women were grouped according to whether they smoked, did not smoke, or lived with a partner who regularly smoked. While they found no difference in the quality of the women's embryos, they noticed a striking difference in embryo implantation and pregnancy rates between the three groups. The implantation rate among non-smokers was 25 per cent, whereas among the other two groups it was only around 12 per cent. Among the non-smokers, the pregnancy rate per embryo transfer was around 48 per cent. Among the smokers, it decreased to 19 per cent, and the 'side-stream smokers' had a pregnancy rate of 20 per cent.
The researchers pointed out that this was a retrospective study that relied on women self-reporting their smoking habits and that more work would have to be done to produce conclusive evidence. However, they concluded that the evidence from the study is clear enough to show the damaging effects of passive smoking on fertility and suggest that all patients be warned of the potential hazards. Professor Warren Foster, director of IVF and reproductive biology at McMaster University's department of obstetrics and gynaecology, said that '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'.
The researchers now hope to undertake a prospective study to try and confirm their results. Meanwhile, they are trying to work out why the embryos from the three different groups of women all seemed to be of similar quality, yet showed distinctive differences in their ability to implant and go on to establish a pregnancy. They believe this might possibly be because cigarette smoke compromised the egg in some way, but that the 'lethal' results did not become apparent until later in embryonic development.
Dr Richard Kennedy, spokesman for the British Fertility Society, said that from such a small study it would be 'premature' to say that passive smoking was as damaging to fertility as smoking. But, he added, 'it is already established that smoking adversely affects IVF outcome and fertility so I am not surprised by the findings'.