Alcohol can be harmful to a fetus due to its ability to easily cross the placental barrier, exposing the developing fetus to its toxic effects [2]. This exposure can lead to a range of disorders known as Fetal Alcohol Spectrum Disorders (FASDs) [2].

The National Health Service (NHS) explains that when a woman drinks during pregnancy, the alcohol in her blood passes through the placenta and reaches the developing baby [3]. This can interfere with the baby's development, especially during the first three months of pregnancy, a critical period of organ formation [3].

The Centers for Disease Control and Prevention (CDC) further details that drinking alcohol during pregnancy can cause brain damage and growth problems in the baby [2]. The more alcohol a woman drinks, the greater the risk to the baby [2].

It's important to note that there is no known safe amount of alcohol to drink while pregnant [3]. The NHS advises that the safest approach is not to drink alcohol at all while you're pregnant [3]. This advice is supported by the American College of Obstetricians and Gynecologists, who recommend abstinence from alcohol during pregnancy due to the risk of fetal harm [1].

In summary, alcohol is harmful to a fetus because it can easily pass through the placenta, exposing the fetus to its toxic effects. This exposure can lead to a range of disorders known as Fetal Alcohol Spectrum Disorders (FASDs), and there is no known safe amount of alcohol to drink while pregnant.

Sources:
[1] <https://www.drugpatentwatch.com/p/tradename/ALCOHOL>
[2] <https://www.cdc.gov/ncbddd/fasd/alcohol-use.html>
[3] <https://www.nhs.uk/pregnancy/keeping-well/drinking-alcohol-while-pregnant/>