1 in 750 infants are born in the United States with fetal alcohol syndrome each year. Meaning the effects that these infants suffer from are low birth weight, small head circumference, developmental delay, facial abnormalities, poor coordination and social skills, and learning disabilities. Fetal alcohol syndrome is the leading known cause of mental retardation and birth defects, although, it is 100% preventable. Prenatal alcohol exposure does not always lead to fetal alcohol syndrome, but there is no proven level of alcohol consumption that is safe. There is no safe level, because there are many other factors that vary the results such as individual women's ability to process alcohol, age of mother, and the regularity of alcohol consumption. Alcohol consumption is dangerous to the fetus because alcohol passes easily through the placental barrier and the fetus is less likely to eliminate the alcohol from their system therefore leaving a high concentration of alcohol in their system. It has been shown that mother's who drink in their first trimester have children with the most severe fetal alcohol syndrome. Because fetuses are constantly changing and developing, the best way to prevent infants from having birth defects is to not consume alcohol during pregnancy.