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Why can alcohol use during pregnancy harm a developing fetus?

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Six small glasses of craft beer in varying amber and golden hues are arranged on a metal tray atop a wooden bar counter in Brussels, Belgium. — Beer Glasses of beer in a bar in Brussels.

Alcohol consumption during pregnancy can harm a developing fetus because ethyl alcohol (ethanol) and its breakdown product, acetaldehyde, are toxic substances that can interfere with the development of the embryo or fetus.1

Exposure to alcohol during this critical period can lead to fetal alcohol syndrome (FAS) and other conditions within the fetal alcohol spectrum disorder (FASD) range. These conditions may result in:21

Physical Abnormalities: Retarded growth, microcephaly, characteristic facial features (such as a thin upper lip and small eye openings), and defects in the heart, joints, and limbs.134
Neurological and Behavioral Impairments: Intellectual disability, delayed development, poor concentration, impulsiveness, and difficulty understanding cause and effect.21

Medical experts emphasize that no amount of alcohol can be considered safe during pregnancy, as even occasional or low-dose consumption may endanger the fetus. Consequently, total abstinence is strongly advised for those who are pregnant or planning to conceive.13