**Core Concept**
The question tests the knowledge of contraindications of anti-tubercular drugs in pregnancy. **Ethambutol**, **Isoniazid**, **Pyrazinamide**, and **Rifampicin** are commonly used anti-tubercular drugs, but their safety profiles vary during pregnancy.

**Why the Correct Answer is Right**
Rifampicin is a potent inducer of the cytochrome P450 enzyme system and can cause fetal hemolysis by inducing the breakdown of fetal red blood cells. Additionally, Rifampicin can displace bilirubin from albumin, potentially causing kernicterus in the newborn. Due to these risks, Rifampicin is generally contraindicated in pregnancy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Isoniazid is not contraindicated in pregnancy, but it requires pyridoxine supplementation to prevent peripheral neuropathy.
* **Option B:** Pyrazinamide is not contraindicated in pregnancy, but it can cause hyperuricemia and gout in some patients.
* **Option C:** Ethambutol is not contraindicated in pregnancy, but it can cause optic neuritis, which may be irreversible.

**Clinical Pearl / High-Yield Fact**
When treating tuberculosis in pregnant women, it is essential to use a combination of drugs that are safe and effective, including Isoniazid, Pyrazinamide, and Streptomycin (if necessary). Rifampicin should be avoided due to its potential risks to the fetus.

**Correct Answer:** C. Pyrazinamide