Fetal alcohol syndrome (FAS) is a disorder of permanent birth defects that occurs in the offspring of women who drink alcohol during pregnancy. It is unknown whether amount, frequency or timing of alcohol consumption during pregnancy causes a difference in degree of damage done to the fetus. Thus, the current recommendation is not to drink at all during pregnancy. Alcohol crosses the placental barrier and can stunt fetal growth or weight, create distinctive facial stigmata, damage neurons and brain structures, and cause other physical, mental, or behavioral problems.Ulleland, C.N. (1972). The offspring of alcoholic mothers. Annals New York Academy of Sciences, 197, 167-169. PMID 4504588Lemoine, P., Harousseau, H., Borteyru, J.B., & Menuet, J.C. (1968). Les infants des parents alcooliques. Anomalies observees, a propos de 127 cas. Quest Medical, 21, 476-482. PMID 12657907Streissguth, A. (1997). Fetal Alcohol Syndrome: A Guide for Families and Communities. Baltimore: Brookes Publishing. ISBN 1-55766-283-5. Over 16% of women drink enough alcohol to be at risk of bearing children with fetal alcohol syndrome. The main effect of FAS is permanent central nervous system damage, especially to the brain. Developing brain cells and structures are underdeveloped or malformed by prenatal alcohol exposure, often creating an array of primary cognitive and functional disabilities (including poor memory, attention deficits, impulsive behavior, and poor cause-effect reasoning) as well as secondary disabilities (for example, mental health problems, and drug addiction).Streissguth, A.P., Barr, H.M., Kogan, J., & Bookstein, F.L. (1996). Understanding the occurrence of secondary disabilities in clients with fetal alcohol syndrome (FAS) and fetal alcohol effects (FAE): Final report to the Centers for Disease Control and Prevention on Grant No. RO4/CCR008515 (Tech. Report No. 96-06). Seattle: University of Washington, Fetal Alcohol and Drug Unit. The risk of brain damage exists during each trimester, since the fetal brain develops throughout the entire pregnancy.

Fetal alcohol exposure is the leading known cause of mental retardation in the Western world. In the United States the FAS prevalence rate is estimated to be between 0.2 and 2.0 cases per 1,000 live births, comparable to or higher than other developmental disabilities such as Down syndrome or Spina Bifida. The lifetime medical and social costs of each child with FAS are estimated to be as high as US$800,000. While prenatal alcohol exposure does not automatically result in FAS, the U.S. Surgeon General advises pregnant women to abstain from alcohol use due to the risk of the syndrome.U.S. Surgeon General Releases Advisory on Alcohol Use in Pregnancy. United States Department of Health and Human Services. Press release (February 21 2005). Retrieved on 2007-04-11