OHSS (Ovarian Hyperstimulation Syndrome)

OHSS occurs when the ovaries over-respond to stimulation medications, producing many follicles. After the hCG trigger, vascular permeability increases, causing fluid to leak from blood vessels into the abdomen and chest. Mild OHSS causes bloating and pelvic discomfort; severe cases involve large ovarian cysts, massive ascites, hemoconcentration, and rarely thrombosis or respiratory distress.

Risk factors include young age, low body weight, PCOS, high AFC, and high estradiol response. Prevention strategies include dose reduction, coasting, using a GnRH agonist trigger instead of hCG, and elective freeze-all (no fresh transfer). Severe OHSS requires hospitalization with IV fluids, albumin, and drainage of ascites. Most cases resolve within 1–2 weeks.