Men who smoke are less likely to make a woman pregnant than nonsmokers, and the more they smoke the worse their chances are, a new study finds. Researchers from the state university at buffalo school of medicine say that male smokers experience changes in their sperm that make fertilization more difficult. The study was presented last week at a conference of the american society of reproductive medicine. Cigarette smoking can also affect male fertility: smoking reduces the quality of semen. Men who smoke have a lower sperm count than non-smokers, and their semen contains a higher proportion of malformed sperm. By-products of nicotine present in semen of smokers have been found to reduce the motility of sperm. One study found that sperm damaged by smoking may also result in more couples having baby girls than boys. The researchers suggest that the sperm cells carrying the y chromosome are more vulnerable to the toxins in cigarette smoke.