Final answer:
A pregnant woman should avoid excessive intake of Vitamin A because it can build up to toxic levels and potentially cause birth defects.
Step-by-step explanation:
A pregnant woman should avoid excessive intake of Vitamin A. While some nutrients like folic acid, calcium, iron, and omega-3 fatty acids are particularly important during pregnancy and must be consumed in adequate amounts, Vitamin A is fat-soluble and can build up to toxic levels in the body if taken in excess. It is essential to provide sufficient folic acid during the early stages of pregnancy to reduce the risk of neurological defects like spina bifida, but Vitamin A can cause birth defects if consumed in high amounts.