Final answer:
It is important for a pregnant woman to avoid all medications unless prescribed by a physician who knows she is pregnant, as medications can have adverse effects on the fetus.
Step-by-step explanation:
A pregnant woman should avoid all medications unless they are prescribed by a physician who knows she is pregnant because medications often have adverse effects when taken during pregnancy. The placenta allows most medications to cross into the fetus, which can potentially harm the developing baby. Taking medications during pregnancy can increase the risk of birth defects and other complications. It is important for pregnant women to receive prenatal care and discuss any medications they are taking with their healthcare provider.