Question

when are teratogens—substances that can cause physical damage or defects—most dangerous to a fetus?
multiple choice
○ during the third trimester
○ during the second trimester
○ just prior to implantation
○ during the first trimester

Explanation:

Teratogens cause fetal defects most when organs form. The first trimester is the critical period of organogenesis—major body structures (e.g., brain, heart, limbs) develop rapidly then, making fetuses highly vulnerable to teratogen-induced damage.

Answer:

during the first trimester