Final answer:
A primary symptom of fetal alcohol syndrome (FAS) is abnormal facial development, including a smooth philtrum, thin upper lip, and small eye openings, resulting from prenatal alcohol exposure.
Step-by-step explanation:
One of the primary signs of fetal alcohol syndrome (FAS) is abnormal facial development. Specific facial features associated with FAS include a smooth philtrum (the area between the nose and upper lip), a thin upper lip, and small eye openings. These characteristics are a result of prenatal alcohol exposure, which is a known teratogen, and can have detrimental effects on the fetus during critical developmental periods.
Notably, exposure during early stages of pregnancy is especially harmful. Cognitive, developmental, and behavioral problems may also be present due to alcohol's teratogenic effects on the fetal brain. Fetal alcohol spectrum disorders, including FAS, are entirely preventable by avoiding alcohol consumption during pregnancy.