## Core Concept
The question tests knowledge of vaccine administration during pregnancy, focusing on safety and recommendations. Certain vaccines are contraindicated in pregnancy due to theoretical risks of transmission or effects on the fetus. Live attenuated vaccines are generally avoided in pregnant women due to the potential risk of transmission to the fetus.

## Why the Correct Answer is Right
The correct answer, **B. BCG (Bacillus Calmette-Guérin)**, is a live attenuated vaccine. Live vaccines are generally contraindicated in pregnancy because of the theoretical risk of transmission of the vaccine virus to the fetus. BCG vaccine is used to protect against tuberculosis and is administered to infants in countries with high TB prevalence. Its live attenuated nature makes it risky for pregnant women.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not specified, but if it were a killed or inactivated vaccine, it would likely be safe for administration during pregnancy.
- **Option C:** This option is not specified, but many conjugate or polysaccharide vaccines are safe and sometimes recommended during pregnancy to protect against infections like pneumococcal disease or meningitis.
- **Option D:** This option is not specified, but similar to option C, if it represents a vaccine that is not live and is used for essential protection during pregnancy (e.g., influenza, Tdap), it would not be contraindicated.

## Clinical Pearl / High-Yield Fact
A key point to remember is that live vaccines, such as **BCG**, **MMR (Measles, Mumps, and Rubella)**, and **Varicella**, are generally avoided in pregnancy. Inactivated or killed vaccines, like the **influenza vaccine**, are recommended to protect pregnant women from infections.

## Correct Answer: B. BCG (Bacillus Calmette-Guérin)