Fetal alcohol syndrome, birth defects, and low birth weight are among the problems associated with alcohol consumption during pregnancy, Dr. C. H Denny and co-authors note in the CDC's Morbidity and Mortality Weekly Report.

To examine trends in alcohol use among women of childbearing age, the researchers analyzed data from 533,506 women 18 to 44 years of age surveyed during 1991-2005; of these, 22,027 were pregnant at the time of the interview.

Any alcohol use was defined as having at least one drink in the past 30 days, and binge drinking as having five or more drinks on at least one occasion in the past 30 days.

"The prevalence of any alcohol use and binge drinking...did not change substantially over time," the authors report.

Among pregnant women, the average annual percentage of any alcohol use was 12.2 percent, while the average annual percentage for binge drinking was 1.9 percent.

Corresponding rates among non-pregnant women were 53.7 percent and 12.1 percent.

Denny's team found that problem drinking among pregnant women was tied to older age, having a college degree, being employed, and being unmarried.

As to why these factors are associated with drinking in pregnancy, the authors of an editorial note suggest that "1) older women might be more likely to be alcohol dependent and have more difficulty abstaining from alcohol while pregnant; 2) more educated women and employed women might have more discretionary money for the purchase of alcohol; and 3) unmarried women might attend more social occasions where alcohol is served."