LONDON (Reuters) - Heavy smokers are less likely to become pregnant through IVF treatment, even with donated eggs, fertility experts said on Thursday.

They found that smoking more than 10 cigarettes a day makes the womb less receptive to the embryo and reduces the odds that it will implant and result in a pregnancy.

Smoking has been known to affect a woman's fertility but Dr Sergio Soares, of the IVI Clinic in Lisbon and his team believe their findings are the first to show heavy smoking has an independent impact on the uterus.

"Cigarette smoking negatively affects pregnancy probability even when the eggs come from a non-smoker," he told Reuters. "This is the first time an effect of tobacco consumption has been demonstrated on the uterus."

He added that even if fertilisation takes place, heavy smokers have less chance of achieving a successful pregnancy.

The scientists compared the success rates of in-vitro fertilisation (IVF) treatments using donated eggs on 44 heavy smokers who puffed more than 10 cigarettes a day and 785 women who did not smoke or were light smokers.

All the women were married to non-smokers.

"The non-heavy smokers had a significantly higher pregnancy rate, with over half becoming pregnant (52.2 percent), compared with just over a third (34.1 percent) of the heavy smokers," Soares said.

He added that the findings, which are published in the journal Human Reproduction, show light smoking did not have any impact on the receptiveness of the uterus to the embryo.

Although heavy smokers were less likely to get pregnant, paradoxically there was a higher multiple pregnancy rate among them. Sixty percent of the heavy smokers had multiple births compared to 31 percent in the other group.

Soares said larger studies are needed to determine if components in tobacco affect the womb differently in various women -- impairing implantation in some women and having the reverse effect in others.

"It is already known that there is paradoxical dose-dependent effect of nicotine on ovarian tissue. Maybe the same effect is happening in uterine tissues," he added.

In addition to impairing fertility, smoking has also been shown to increase the risk of heart attack and stroke, respiratory problems and lung and other cancers.

Despite its macho advertising image, a recent study showed that men who smoked were more likely to suffer from impotence.