Alcohol use during pregnancy can cause fetal alcohol spectrum disorders (FASDs), which are physical, behavioral, and intellectual disabilities that last a lifetime. More than 3 million US women are at risk of exposing their developing baby to alcohol because they are drinking, having sex, and not using birth control to prevent pregnancy. About half of all US pregnancies are unplanned and, even if planned, most women do not know they are pregnant until they are 4-6 weeks into the pregnancy.

CDC: http://www.cdc.gov/vitalsigns/fasd/