**Core Concept**
Ovarian Hyperstimulation Syndrome (OHSS) results from excessive ovarian response to exogenous gonadotropins, leading to vascular leakage, fluid accumulation, and ovarian enlargement. The pathogenesis involves angiogenic factors like VEGF and inflammatory cytokines, which disrupt vascular integrity.

**Why the Correct Answer is Right**
OHSS is primarily driven by overstimulation of ovarian follicles during fertility treatments, resulting in massive ovarian enlargement and fragility. Vascular permeability increases due to elevated **vascular endothelial growth factor (VEGF)** and inflammatory cytokines (e.g., IL-6, TNF-α), causing fluid shift into the peritoneal cavity. Ovarian enlargement is a hallmark, and the condition is strongly linked to infertility treatments like IVF. However, **increased intravascular volume** is not a feature — instead, fluid shifts from intravascular to extravascular spaces due to vascular leakage, leading to hypovolemia and decreased circulating volume.

**Why Each Wrong Option is Incorrect**
Option A: Ovarian enlargement and fragility are central to OHSS pathology; this is true.
Option C: VEGF and inflammatory cytokines are key mediators of vascular leakage and pathogenesis — this is true.
Option D: OHSS is a known complication of infertility treatments, especially IVF — this is true.

**Clinical Pearl / High-Yield Fact**
OHSS is a life-threatening condition that can progress from mild to severe; early recognition is vital. **VEGF is the most significant mediator** of vascular permeability. Always suspect OHSS in patients with high ovarian response to stimulation.

✓ Correct Answer: B. Increase in intravascular volume