**Core Concept**
Pregnancy-induced hypertension (PIH) is a condition characterized by new-onset hypertension and proteinuria after 20 weeks of gestation. It can lead to significant changes in renal function, including glomerular filtration rate (GFR). The underlying mechanism involves endothelial dysfunction, vascular remodeling, and the release of various vasoactive substances.

**Why the Correct Answer is Right**
PIH leads to a decrease in GFR due to the activation of the renin-angiotensin-aldosterone system (RAAS), increased sympathetic tone, and the release of vasopressin. These factors cause vasoconstriction of the afferent and efferent arterioles, which reduces renal blood flow and glomerular hydrostatic pressure, ultimately decreasing GFR. Additionally, the increased levels of anti-angiogenic factors such as soluble fms-like tyrosine kinase-1 (sFlt-1) and decreased levels of pro-angiogenic factors like placental growth factor (PlGF) contribute to endothelial dysfunction and further compromise renal function.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because PIH does not typically cause an increase in GFR. While some studies suggest a transient increase in GFR in early pregnancy, PIH leads to a decrease in GFR due to the mechanisms mentioned above.
* **Option B:** Incorrect because PIH does not directly affect the glomerular filtration barrier, which is primarily responsible for the filtration of waste products from the blood. The decrease in GFR is a result of the vasoconstrictive effects of PIH on the renal vasculature.
* **Option C:** Incorrect because PIH does not typically cause an increase in renal blood flow. While some studies suggest a transient increase in renal blood flow in early pregnancy, PIH leads to a decrease in renal blood flow due to the vasoconstrictive effects of the RAAS and other vasoactive substances.

**Clinical Pearl / High-Yield Fact**
In patients with PIH, careful monitoring of renal function is essential to prevent acute kidney injury (AKI). The use of angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) should be avoided in these patients due to the risk of further decreasing GFR and exacerbating AKI.

**Correct Answer:** B.