Smouldering cigarettes can be just as damaging as Smoking to women having fertility treatment, a new study suggests on Thursday.

Doctors know that smoking can affect a woman’s fertility and damage sperm but scientists in Canada have found that exposure to second-hand smoke can affect the success rates of treatments such as in-vitro fertilisation (IVF).

In a study that compared the outcomes of fertility treatment, they found smokers and women who lived with smokers had about a 20 percent pregnancy rate per embryo transfer, compared to 48 percent for non-smokers.

“Although we do need a prospective confirmatory study, the findings from our study warrant a warning to women to reduce or, if possible, prevent exposure to cigarette smoking, especially if they are trying to conceive,” said Professor Warren Foster, of McMaster University in Hamilton, Canada.

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 percent implantation rate, both smokers and side-stream smokers managed only around 12 percent.”

Side-stream smoke is emitted from the smouldering end of the cigarette 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 a mean 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. They are planning a further study to try to answer the question.