Which of the following is an effect of teratogens during pregnancy?

Teratogens are substances that can cause abnormalities in a developing fetus when a pregnant individual is exposed to them. One of the most well-known effects of teratogen exposure is fetal alcohol syndrome, which results from the consumption of alcohol during pregnancy. This condition is characterized by a range of physical, behavioral, and cognitive defects that can include facial abnormalities, growth deficiencies, and neurodevelopmental challenges.

Fetal alcohol syndrome exemplifies how a teratogen directly impacts the development of the fetus, highlighting the dangers associated with certain substances during critical periods of development when organs and systems are being formed. As a result, this choice is correct as it distinctly represents the harmful effects that teratogens can have on prenatal development.

In contrast, the other options do not align with the well-documented impacts of teratogens. Improved fetal brain development and enhanced motor skills are positive outcomes that would not typically be associated with teratogen exposure. Additionally, while childhood obesity can have various causes, it is not a direct effect of teratogens during the pregnancy period. Thus, fetal alcohol syndrome stands out as a specific and serious outcome of teratogenic exposure.