Why do the RDAs for calcium and vitamin D generally remain unchanged during pregnancy despite increased fetal needs for calcium?

• A. Pregnancy increases maternal absorption efficiency and alters physiology so that more dietary calcium is absorbed, and vitamin D's role in absorption means its RDA also remains unchanged
• B. Because the fetus obtains calcium exclusively from maternal bone breakdown and not from dietary sources, so dietary RDAs are irrelevant
• C. Because pregnant women are advised to avoid dairy and sun exposure, which balances the demand and supply without changing RDAs
• D. Because the placenta produces large amounts of calcium and vitamin D, eliminating the need for increased maternal intake

Answer: (A)