**Core Concept**
During pregnancy, vaccines are carefully selected to ensure safety for both the mother and the fetus. The decision to administer a vaccine depends on the potential risks and benefits, as well as the critical period of fetal development.

**Why the Correct Answer is Right**
Influenza vaccine is recommended for pregnant women during the flu season to prevent maternal and fetal complications. Inactivated influenza vaccine (IIV) and recombinant influenza vaccine (RIV) are safe to administer during pregnancy. **Option A: Inactivated influenza vaccine (IIV)** is correct because it is composed of killed-virus and does not pose a risk to the fetus.

**Why Each Wrong Option is Incorrect**
**Option B:** Tdap vaccine is not a wrong option as it is safe to administer during pregnancy, usually between 27 and 36 weeks of gestation, to provide protection against pertussis. It is given in place of the Td booster.

**Option C:** Inactivated poliovirus vaccine (IPV) is safe to administer during pregnancy. IPV is composed of inactivated virus and does not pose a risk to the fetus.

**Option D:** Live, attenuated vaccines, such as MMR, varicella, and oral poliovirus vaccine (OPV), are generally contraindicated during pregnancy due to the theoretical risk of transmission of the live virus to the fetus.

**Clinical Pearl / High-Yield Fact**
When selecting vaccines during pregnancy, it is essential to consider the gestational age and the potential risks and benefits of each vaccine.

**Correct Answer: D. Live, attenuated vaccines, such as MMR, varicella, and oral poliovirus vaccine (OPV), are generally contraindicated during pregnancy due to the theoretical risk of transmission of the live virus to the fetus.**