During preconception counseling, the nurse explains that the fetus is most vulnerable to the effects ...

ANS: A
The period of organogenesis lasts from approximately the second until the eighth week of gestation, during which time the embryo undergoes rapid growth and differentiation. During organogenesis, the embryo is extremely vulnerable to teratogens, such as medications, alcohol, tobacco, caffeine, illegal drugs, radiation, heavy metals, and maternal (TORCH) infections. Structural fetal defects are most likely to occur during this period because exposure to teratogens, either before or during a critical period of development of an organ, can cause a malformation.