**Core Concept**
The use of vaccines during pregnancy is a critical consideration due to the potential risks and benefits to both the mother and the fetus. Live attenuated vaccines pose a theoretical risk of transmission to the fetus, whereas inactivated vaccines are generally considered safe. The decision to administer vaccines during pregnancy must be made on a case-by-case basis, taking into account the risks associated with the specific vaccine and the benefits of vaccination.

**Why the Correct Answer is Right**
The Yellow Fever vaccine is an inactivated vaccine, which means it does not contain live, attenuated viruses that can potentially infect the fetus. This makes it a safe option for use during pregnancy, particularly in areas where the risk of yellow fever is high. The vaccine stimulates the production of antibodies that can provide protection against the disease, which is essential for pregnant women traveling to or living in endemic areas. The Yellow Fever vaccine has been extensively studied in pregnant women, and the available data suggest that it is safe and effective.

**Why Each Wrong Option is Incorrect**
**Option A:** BCG Vaccine is a live attenuated vaccine, and its use during pregnancy is generally contraindicated due to the potential risk of transmission to the fetus.
**Option B:** Measles Vaccines are also live attenuated vaccines, and their use during pregnancy is contraindicated due to the risk of transmission to the fetus.
**Option C:** OPV Vaccine is a live attenuated vaccine, and its use during pregnancy is contraindicated due to the risk of transmission to the fetus.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the decision to administer vaccines during pregnancy should be made after careful consideration of the individual risks and benefits, and in consultation with a healthcare provider. Pregnant women should be up-to-date on all recommended vaccinations before conception, and any necessary vaccinations should be administered during pregnancy or postpartum.

**✓ Correct Answer: D. Yellow fever vaccine**