**Core Concept**
The question tests the knowledge of teratogenic effects of anti-retroviral drugs, specifically in the context of HIV management during pregnancy. The correct answer requires understanding of the pharmacological properties of these medications and their implications for fetal development.

**Why the Correct Answer is Right**
Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI) used in the treatment of HIV/AIDS. However, it is known to have teratogenic effects, including neural tube defects and craniofacial abnormalities. Efavirenz is contraindicated in pregnancy due to these risks, and alternative regimens should be considered for pregnant women.

**Why Each Wrong Option is Incorrect**
**Option A:** Nucleoside reverse transcriptase inhibitors (NRTIs) like zidovudine are commonly used in pregnancy and are considered safe.
**Option B:** Protease inhibitors like lopinavir/ritonavir are also used in pregnancy and have a favorable safety profile.
**Option C:** Integrase strand transfer inhibitors (INSTIs) like raltegravir are another class of anti-retroviral drugs that are considered safe in pregnancy.

**Clinical Pearl / High-Yield Fact**
It's essential for clinicians to be aware of the teratogenic potential of medications, including anti-retroviral drugs, and to carefully weigh the risks and benefits for pregnant women. In the case of efavirenz, alternative regimens should be considered to minimize the risk of fetal harm.

**Correct Answer:** C. Efavirenz.