Women who smoke heavily have a much harder time getting pregnant via in-vitro fertilization, researchers say.

Reuters reported Nov. 9 that a study found that smoking made the womb less receptive to embryo implantation. And even if the embryo did implant successfully, heavy smokers were less likely to have a successful pregnancy than nonsmokers.

The problems were observed among women who smoked 10 or more cigarettes daily.

"Cigarette smoking negatively affects pregnancy probability even when the eggs come from a nonsmoker," said fertility expert Sergio Soares. "This is the first time an effect of tobacco consumption has been demonstrated on the uterus."

The research appears online in the journal Human Reproduction.