**Core Concept**
High doses of Vitamin A are known teratogens, meaning they can cause congenital abnormalities in developing fetuses. This is due to the fact that retinoic acid, a derivative of Vitamin A, plays a crucial role in embryonic development.

**Why the Correct Answer is Right**
Vitamin A is a fat-soluble vitamin that is essential for various bodily functions, including vision, immune function, and reproduction. However, excessive intake of Vitamin A during pregnancy can lead to teratogenic effects, resulting in birth defects such as craniofacial abnormalities, heart defects, and central nervous system malformations. The mechanism behind this involves the disruption of embryonic development, particularly during the critical periods of organogenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin C is an essential nutrient that plays a crucial role in collagen synthesis, iron absorption, and immune function. It is not known to cause teratogenic effects when taken in recommended doses.
**Option B:** Vitamin E is another essential nutrient that acts as an antioxidant in the body, protecting cells from damage. It is not associated with teratogenic effects.
**Option D:** Vitamin D is essential for calcium absorption and bone health. While excessive intake of Vitamin D can cause toxicity, it is not known to cause teratogenic effects.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the teratogenic effects of Vitamin A are dose-dependent, and the risk of birth defects increases with higher doses. Pregnant women should avoid taking high-dose Vitamin A supplements and instead follow the recommended dietary allowance.

✓ Correct Answer: C. Vit. A