Hamilton: Passive smoking can be just has harmful as smoking to women having fertility treatment.

In a study that compared the outcomes of fertility treatment, researchers at the McMaster University, Hamilton, Canada, found smokers and women who lived with smokers had about a 20 per cent pregnancy rate per embryo transfer in IVF treatment, compared to 48 per cent for non-smokers.

The researchers, who reported their findings in the journal Human Reproduction, said there was no difference in the quality of the embryos from the three groups of women but they found a vast variation in the number of embryos that successfully implanted in the womb.

“This was the most striking finding from our study,” said lead researcher Michael Neal. “When it came to implantation rates … we found that while non-smokers achieved a 25 per cent implantation rate, both smokers and side-stream smokers managed only around 12 per cent.”

Side-stream smoke is emitted from smouldering cigarettes and contains the most toxic constituents. Passive smoking includes side-stream smoking and smoke exhaled by the woman’s partner.

Smokers in the study smoked an average of 11 cigarettes a day.

The researchers do not understand why there is such a difference in implanting and maintaining a pregnancy in the smoking groups, despite the good quality and appearance of the embryos.