## **Core Concept**
The question tests knowledge of anti-tuberculosis (TB) drugs and their safety profiles during pregnancy. Certain anti-TB drugs are known to have teratogenic effects or other adverse outcomes in pregnant women, making their use critical to consider in this population.

## **Why the Correct Answer is Right**
The correct answer, **Ethambutol** is not typically the most concerning, but **Isoniazid (INH)**, **Rifampicin**, and **Pyrazinamide** have specific considerations. However, **Streptomycin**, an aminoglycoside antibiotic used to treat TB, is notably contraindicated in pregnancy due to its potential to cause **ototoxicity** in the fetus, leading to congenital deafness. This is a critical consideration because the risk of ototoxicity and potential harm to the fetus outweighs the benefits of using streptomycin during pregnancy.

## **Why Each Wrong Option is Incorrect**
- **Option A: Isoniazid (INH)** is used with caution and is actually considered relatively safe in pregnancy with pyridoxine supplementation to prevent neuropathy.
- **Option B: Rifampicin** is also used with caution but is generally not contraindicated; it's considered to have a relatively good safety profile.
- **Option C: Ethambutol** is considered relatively safe during pregnancy but requires monitoring for optic neuritis.
- **Option D: Pyrazinamide** is used unless there's liver disease; its safety profile isn't as clear-cut as streptomycin's but isn't the best answer here.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **streptomycin** is an aminoglycoside and its use in pregnancy can lead to **fetal ototoxicity**. Pregnant women with TB usually require a combination of drugs but are carefully selected to avoid teratogenic effects.

## **Correct Answer: D. Streptomycin**