About 35 percent of women in Kentucky who could be pregnant smoke, the highest rate in the nation, a government report finds.

Kentucky, a tobacco-producing state, has the largest number of women smokers in the U.S. ages 18 to 44, according to the Centers for Disease Control and Prevention. Overall, almost a quarter of U.S. women of the same age group smoke, the report found.

Keeping women of childbearing age from smoking is critical because many don't realize they're pregnant until they're 6 to 8 weeks along, said Matthew McKenna, the director of the CDC's Office of Smoking and Health in Atlanta. Tobacco smoke can cause low birth weight, stillbirth, and sudden infant death syndrome. It's also linked to infertility and spontaneous abortion, the report said. Pregnancy complications due to smoking cost the U.S. $366 million a year, according to CDC data.