**Core Concept**
The use of certain medications during pregnancy can lead to congenital abnormalities in the fetus. This question requires knowledge of teratogenic effects of various drugs on fetal development.

**Why the Correct Answer is Right**
Warfarin, an anticoagulant, is known to cause warfarin embryopathy when taken during pregnancy, particularly during the first trimester. This condition is characterized by nasal hypoplasia and stippling of the bones (also known as "chondrodysplasia punctata"). Warfarin acts by inhibiting vitamin K-dependent enzymes, such as gamma-glutamyl carboxylase, which are essential for the production of clotting factors and the calcification of cartilage.

**Why Each Wrong Option is Incorrect**
* **Option A:** Methotrexate is a teratogen that can cause craniofacial abnormalities, growth restriction, and central nervous system defects. However, it is not specifically associated with warfarin embryopathy.
* **Option B:** Lithium is known to cause cardiac malformations, particularly Ebstein's anomaly, but it is not linked to warfarin embryopathy.
* **Option C:** Tetracycline antibiotics can cause tooth discoloration and inhibit bone growth, but they are not associated with warfarin embryopathy.

**Clinical Pearl / High-Yield Fact**
To avoid warfarin embryopathy, pregnant women should be switched to alternative anticoagulants, such as heparin, as soon as possible if they require anticoagulation therapy.

**Correct Answer: C. Warfarin**