Smoking appears to damage the success rate of both standard IVF techniques and ICSI, which involves injecting a sperm directly into an egg to achieve fertilisation.

Dr Michael Zitzmann told the European Society of Human Reproduction and Embryology annual conference in Vienna that smoking altered the DNA of sperm and he believed this hampered the development of the embryo.

Dr Zitzmann's team from the Institute of Reproductive Medicine in M�nster, Germany, studied 301 couples, of whom 153 were receiving ICSI treatment and 148 were receiving IVF treatment.

Among those receiving ICSI treatment, 71 men were habitual smokers, and in the IVF group 68 men were smokers.

Sizeable effect

In the ICSI group, 22% of the women with smoking partners became pregnant, compared to 38% of women with non-smoking partners.

The chances of the whole procedure failing and no pregnancy occurring was two to three times higher in smoking men

Dr Michael Zitzmann, Institute of Reproductive Medicine, M�nster

In the IVF group the results were similar, with 18% of women with smoking partners becoming pregnant compared to 32% of women whose partners were not smokers.

If the woman smoked, the number of eggs capable of being retrieved from her ovaries dropped significantly from an average of 11.7 per cycle to 9.5.

The chances of the eggs being successfully fertilised also dropped.

Dr Zitzmann said: "These results show that men who smoke, significantly decrease the success rates of assisted reproduction procedures, not only in IVF, but also in ICSI.

"The chances of the whole procedure failing and no pregnancy occurring was two to three times higher in smoking men compared with non-smokers.

"Smoking probably has an adverse effect during the fertilisation procedure, but, in addition, smoking damages the DNA in sperm and this may hamper the development of the embryo."

Long-term effect

Dr Zitzmann said smoking represented a needless risk to women undergoing futile hormonal stimulation - and meant that couples were more likely to waste their money.

He said: "It can be assumed that quitting smoking will be beneficial to couples undergoing IVF or ICSI.

"However, we do not know how long the damaging effects of smoking last after quitting as our study did not investigate this."