A pregnant teenager asks the clinic nurse why she cannot smoke during the first trimester.Remembering growth and development,what is the nurse's best response?

A) "Smoking is a bad habit, but it probably won't affect the baby."
B) "Smoking may affect organ systems that are beginning to develop."
C) "Smoking will only affect the baby in the third trimester."
D) "Smoking mothers usually produce overweight babies"

Teratogens are chemical or physiological agents capable of having adverse effects on the fetus.Exposure to potential teratogens can affect fetal development during any of the trimesters; however,vulnerability is increased during the first trimester when fetal cells are differentiating and organs are forming.In addition,there is evidence that mothers who smoke deliver infants with lower birth weights than nonsmoking mothers.