A new study finds that women who smoke are more likely to give birth to female babies, adding weight to a theory that smoking may cause disproportionate harm to male fetuses, the Independent reported April 9.

Women in Western countries usually give birth to more boys than girls -- about 52 percent of newborns are male. But women who smoke during pregnancy are one-third less likely to give birth to boys than nonsmokers, and the odds of having a boy are cut in half if the father also smokes.

Some studies suggest that smoking not only makes it harder to conceive male children but may prevent male embryos from implanting in the uterus and leads to miscarriages. Researchers who studied 9,000 women who delivered babies at Liverpool Women's Hospital also found that mothers exposed to secondhand smoking by their partners also were less likely to have boys.

The research was conducted at the Liverpool (U.K.) School of Tropical Medicine and led by professor Bernard Brabin. The findings were presented at a meeting of the Royal Academy of Pediatrics and Child Health.