**Core Concept**
Pregnancy-induced hypertension (PIH) affects renal function by altering the dynamics of renal blood flow and glomerular filtration rate (GFR). The underlying pathophysiological mechanism involves vasoconstriction of the renal arteries, leading to decreased perfusion of the glomeruli.

**Why the Correct Answer is Right**
During PIH, the increased vascular resistance and decreased blood flow to the kidneys result in a reduction in GFR. This is due to the activation of the renin-angiotensin-aldosterone system (RAAS) and the release of vasopressin, which cause vasoconstriction of the renal arteries. The decreased GFR can lead to a decrease in the clearance of waste products, such as urea, and can also affect the clearance of medications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PIH typically does not cause an increase in GFR.

**Option B:** This option is incorrect because while PIH can cause changes in the renal vasculature, it is not primarily characterized by an increase in renal blood flow.

**Option C:** This option is incorrect because PIH can cause a decrease in GFR due to vasoconstriction of the renal arteries, but it is not primarily characterized by an increase in the glomerular filtration rate.

**Clinical Pearl / High-Yield Fact**
In PIH, the decreased GFR can lead to a decrease in the clearance of waste products, such as urea, and can also affect the clearance of medications. This can result in increased levels of these substances in the blood, leading to potential toxicity.

**Correct Answer: D. Decrease in GFR**