## Core Concept
The renal system undergoes significant changes during pregnancy to accommodate the increased metabolic demands and to ensure proper filtration and excretion. These changes include increases in renal blood flow, glomerular filtration rate (GFR), and alterations in electrolyte and water handling.

## Why the Correct Answer is Right
The correct answer states that there is no significant decrease in GFR during pregnancy; rather, GFR increases by about 50% by the end of the first trimester and continues to increase throughout pregnancy. This increase supports the higher metabolic rate and helps in the elimination of waste products. The renal blood flow also increases significantly, contributing to the elevated GFR.

## Why Each Wrong Option is Incorrect
- **Option A:** Increase in renal blood flow and GFR are true changes; they are crucial for handling the increased load of waste products and for the overall health of the mother and fetus.
- **Option B:** Changes in electrolyte handling, such as increased excretion of sodium and water retention, are adaptations to pregnancy; they support the expansion of maternal blood volume.
- **Option C:** Alterations in the renal anatomy, such as ureteral dilation, can occur due to the mechanical effects of the enlarging uterus; this can sometimes lead to issues like hydronephrosis.
- **Option D:** A decrease in GFR is not a characteristic change of pregnancy; this would be harmful and is not observed.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the increase in GFR during pregnancy affects the levels of various substances in the blood, including creatinine and urea, which are typically lower than in the non-pregnant state. This change is important when interpreting laboratory results in pregnant women.

## Correct Answer: D. Decrease in GFR.