The smoker's sperm samples were tested against one half of the egg covering, while the non-smokers were tested against the other half. Success was judged by the ability of the sperm to stick to this outer coating.
In the time it takes reproductive cells to work their magic, two-thirds of the sperm samples choked by tobacco smoke failed to pierce the outer layer of the female egg, suggesting that smokers would have a tougher time causing a pregnancy. Overall, men who smoked 18 or more cigarettes a day for at least two years had about one quarter of the fertilization power as non-smokers.
Those who smoked less had better functioning sperm, suggesting that guys may not have to go cold turkey to improve their chances.
"If we can get men to cut down to five or six cigarettes a day, they can increase their fertility," said Burkman.
Just the same, the findings point to yet another reason to kick the habit, the sooner the better.
"We always want people to quit smoking," Burkman said.