- Excessive intake of vitamin A during pregnancy is well-known to cause teratogenic effects, particularly affecting the development of the craniofacial region and the central nervous system (CNS).
- Vitamin A is a fat-soluble vitamin essential for normal growth and development, but in high doses, it disrupts normal embryonic morphogenesis.

The teratogenicity is primarily due to the role of retinoic acid, an active metabolite of vitamin A, which regulates gene expression during embryogenesis. Excessive retinoic acid can lead to malformations such as cleft palate, microcephaly, hydrocephalus, and other CNS abnormalities.

In contrast:
- Vitamin D toxicity mainly causes hypercalcemia and related symptoms.
- Vitamin B12 excess is rare and not associated with teratogenicity.
- Vitamin E overconsumption is generally not linked to major congenital defects.

Therefore, the correct answer is Vitamin A.

Reference: Medical Physiology, 3rd Edition, Volume 1, Chapter 45: Vitamins and Minerals - Page 720_