**Core Concept:** Glomerular filtration rate (GFR) is the rate at which blood passes through the glomerulus in nephrons of the kidney. A decrease in GFR indicates kidney dysfunction.

**Why the Correct Answer is Right:** In pregnancy, GFR increases due to the following reasons:
1. **Higher cardiac output:** Cardiac output is multiplied during pregnancy, leading to an enhanced blood flow in the kidneys. This results in increased filtration rate.
2. **Hypertension:** Although mild hypertension is common in pregnancy, it does not significantly affect GFR as the increased blood pressure is typically due to vasodilation and higher cardiac output, not elevated blood viscosity.
3. **Increased plasma volume:** The volume of plasma increases by 40-50% during pregnancy, contributing to a higher filtration rate.

**Why Each Wrong Option is Incorrect:**
1. **Option A:** This answer is incorrect because the increased cardiac output and hypertension in pregnancy do not directly cause a decrease in GFR.
2. **Option B:** Although mild hypertension is found in pregnancy, it does not significantly affect GFR, as explained above.
3. **Option C:** This answer is incorrect because the increased plasma volume contributes to the elevated filtration rate, not a decrease.

**Clinical Pearl:** Understanding the physiology behind the increased GFR during pregnancy is crucial to avoid misdiagnosis of kidney dysfunction. A decreased GFR might be mistakenly attributed to pre-eclampsia or other renal diseases, but the clinical context of pregnancy helps differentiate and rule out such conditions.

**Correct Answer:** C. GFR increases during pregnancy due to increased cardiac output, plasma volume, and mild hypertension.