About 12 percent of pregnant women are addicted smokers, and about half of these also had mental-health disorders, the Associated Press reported Sept. 10.

Researchers found that 22 percent of all women smoked at some point during their pregnancy, and that about a third of smokers had a mental-health disorder. By far, the most common mental-health problem reported was depression.

Experts said that depression could complicate efforts to quit, and recommended that prenatal checkups include screening of smokers for mental-health issues.

"These ladies all know, I promise you, about the health risks. That's not what it is," said Jan Blalock of the University of Texas M.D Anderson Cancer Center. "We should at least understand more about why these ladies don't quit." Blalock is running a study called Project Baby Steps, which is looking at whether giving antidepressants to pregnant women helps them quit smoking.

The study by Renee Goodwin of Columbia University and colleagues was published in the April 2007 issue of the journal Obstetrics and Gynecology.