Final answer:
Alcohol is extremely harmful in the first trimester of pregnancy as it can cause fetal alcohol spectrum disorders, including fetal alcohol syndrome, with severe lifelong effects on development.
Step-by-step explanation:
Alcohol consumed in the first trimester is very dangerous. During the first trimester, all of the body's organs and structures are going through initial development. Exposure to alcohol and other toxins can have severe effects on the fetus' survival and development. Alcohol is a teratogen that can cross the placenta and affect the developing embryo or fetus, potentially leading to fetal alcohol spectrum disorders (FASD), with fetal alcohol syndrome (FAS) being the most severe form. These disorders can cause lifelong issues such as cognitive deficits, developmental delays, and distinct facial features including a smooth philtrum and a thin upper lip.