Millions of women could be putting their developing babies at risk because of their drinking habits, the Centers for Disease Control and Prevention says. An estimated 3.3 million women who drink are sexually active but not on birth control, according to a CDC report released Tuesday. And three out of four women who want to get pregnant don't stop drinking alcohol when they stop using birth control. Drinking during pregnancy can lead to fetal alcohol spectrum disorders, a range of behavioral, intellectual, and physical disabilities. There is no known amount of alcohol that's safe to consume while pregnant, according to the agency. "Alcohol can permanently harm a developing baby before a woman knows she is pregnant," CDC principal deputy director Anne Schuchat said in a statement. "About half of all pregnancies in the United States are unplanned, and even if planned, most women won't know they are pregnant for the first month or so, when they might still be drinking. The risk is real. Why take the chance?" The American Academy of Pediatrics last year said no amount of alcohol is safe at any point during a pregnancy. The organization noted the odds of a child's developing FASD increase 12 times when a mother drinks during the first trimester, compared to not drinking at all.