What happens to BUN in early pregnancy as described in the material?

• A. BUN decreases about 50% in the first trimester
• B. BUN increases by 50% in the first trimester
• C. BUN remains unchanged
• D. BUN decreases by 10% in the third trimester

Answer: (A)

In early pregnancy, renal hemodynamics shift: there’s a marked increase in renal plasma flow and GFR, along with plasma volume expansion. This boosts clearance of urea and dilutes serum constituents, so BUN drops substantially. The material notes about a 50% decrease in the first trimester, which best reflects these physiologic changes. The other options don’t fit because BUN does not rise, it does not stay unchanged, and a small 10% decrease in the third trimester doesn’t match the substantial early drop described.