Vitamin B12 is especially recommended for vegetarian or vegan pregnant women because it is primarily found in animal products, making deficiency common in those who avoid these foods. B12 is crucial for fetal neurodevelopment and preventing neural tube defects. Deficiency can lead to megaloblastic anemia and irreversible neurological damage to both the mother and fetus. Supplementation ensures adequate maternal stores and supports healthy pregnancy outcomes.

Reference: Obstetrics: Normal and Problem Pregnancies, Gabbe et al., 7th Edition.