There was a 'striking difference' in implantation and pregnancy rates between non-smokers and the smokers and passive smokers. A couple who are both heavy smokers will have even more difficulty starting a family than if just one partner smokes.

So if she hopes to start a family she should avoid any exposure to cigarettes at all, says Professor Warren Foster of McMaster University and Hamilton Health Sciences in Ontario, Canada.

His study involved 225 women undergoing fertility treatment such as IVF, but he claims the results apply to all women.

'Striking Difference' in Implantation and Pregnancy Rates

The research, published in the journal http://humrep.oupjournals.org/">Human Reproduction, compared the quality of embryos and the implantation and pregnancy rates of non-smokers, smokers or 'side-stream' smokers -- defined as women living with a partner who regularly smoked.

The researchers found there was no difference in embryo quality between the three groups.

But they found there was a 'striking difference' in implantation and pregnancy rates between non-smokers and the smokers and passive smokers.

Researcher Michael Neal said the results were so clear that all patients were being warned about the hazards of passive smoking.

Smoking Reduces Fertility in Both Men and Women

This follows a report from the British Medical Association showing that smoking reduces fertility in both men and women, with women smokers 40 percent less likely to become pregnant than nonsmokers, and twice as likely to be infertile.

It means a couple who are both heavy smokers will have even more difficulty starting a family than if just one partner smokes.