The Centers for Disease Control and Prevention says drinking especially binge drinking can damage fetal brain development.
The CDC numbers are from national telephone surveys that included 14,000 pregnant women. They were asked whether they drank alcohol the previous month and how much.
Of those who said they drank, nearly 1 in 5 said they went on at least one binge downing four or more drinks. Pregnant women ages 35 to 44 were the biggest drinkers.
The good news: Binge drinking among pregnant women is down slightly since a similar study was done in the early 2000s.
The survey results from 2006 through 2010 were released Thursday.