**Core Concept**
Ovarian hyperstimulation syndrome (OHSS) is a complication of ovarian stimulation, often occurring in women undergoing fertility treatments. It is characterized by an exaggerated response to follicle-stimulating hormone (FSH), leading to the overproduction of estrogen and the rupture of ovarian follicles.

**Why the Correct Answer is Right**
The symptoms of OHSS include abdominal pain, nausea, vomiting, diarrhea, and weight gain due to fluid retention. The pathophysiology involves the increased capillary permeability, leading to the leakage of fluid from the blood vessels into the third space. This results in hemoconcentration, electrolyte imbalances, and potentially life-threatening complications. The increased estrogen levels also contribute to the symptoms by causing vasodilation and smooth muscle relaxation.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect as it is not a symptom of OHSS. While patients with OHSS may experience fatigue, it is not a primary symptom.

**Option B:**
This option is incorrect as ascites is a common finding in OHSS, not a cause for concern.

**Option C:**
This option is incorrect as it is a potential complication of OHSS, not a symptom.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of OHSS is the presence of large ovarian cysts, which can rupture and cause severe pain. This is often accompanied by ultrasound findings of multiple follicles and ascites.

**Correct Answer:** A. Fatigue