Smoking can make a woman years older in reproductive terms - significantly reducing her chances of successful IVF treatment, Dutch scientists have said.
More than 40% of the women involved in the study were smokers
Researchers looked at 8,457 women aged 20 to 40 who had had IVF treatment.
A 30-year-old non-smoker had the same chance of conceiving as a 20-year-old smoker, they told Human Reproduction.
Couples having IVF treatment are told smoking can cut success rates but a UK expert said being able to say by how much might encourage more to quit.
However, the researchers did not compare all age groups and warned they could not say if smoking always adds 10 years to a woman's reproductive age, whatever age she actually is.
Experts said it was already known that smoking affected natural fertility.
The Dutch researchers, from 12 hospitals across the Netherlands, looked at data for 8,457 women who had undergone one cycle of IVF treatment between 1983 and 1995.
All had being trying to become pregnant for at least a year.
More than 40% of the women were smokers at the time of undergoing their first attempt at IVF and more than 7% were clinically overweight.
The women were divided into four groups, depending on the cause of each couple's fertility problems; male fertility disorder, fallopian tube problems, other clinical explanations - such as polycystic ovaries or endometriosis, or unexplained fertility problems, known as subfertility.
A total of 1,828 were being treated for unexplained subfertility. The overall live birth rate per cycle was 15.2%.
Older women had lower IVF success rates no matter what the cause of their fertility problems was.
Overall, the live birth rate for smokers was 28% lower than non-smokers.
Among women with unexplained subfertility, the live birth rate was a third lower for smokers, at 13% compared to 20% for non-smokers.
The miscarriage risk was a fifth higher for smokers in this group compared to non-smokers, at 21.4% compared to 16.4%.
Being significantly overweight also cut women's chance of a successful pregnancy by a third.
Professor Didi Braat from Radbound University, who worked on the study, said: "Smoking has a devastating impact."
But she added: "This also indicates that subfertile couples may help their chances of successful treatment by life-style changes.
"As the effects of smoking and being overweight were greatest among women with unexplained subfertility, these results suggest that this group in particular may be able to improve the outcome of subfertility treatment by quitting smoking and losing weight."
Dr Simon Fishel, a specialist at the UK's Care in the Park fertility clinics, said: "We know that smoking reduces a woman's chance of having a live birth and of getting pregnant, and 10 years sounds about right in terms of quantifying the effect.
"One thing couples know is that age is a significant factor in IVF success.
"So if you say to them that by smoking, they give themselves the same chance of success as if they were 10 years older, it brings home to them the effect the habit has."