Ovarian hyperstimulation syndrome (OHSS) is a condition in which the ovaries become large, swollen, and often painful. The most common cause is as a complication of fertility drugs used to stimulate multiple follicle growth. Rare cases can occur spontaneously without any prior medical interventions.

OHSS is caused by increased follicle growth in conjunction with high levels of estradiol. The exact pathophysiology is unknown but is thought to be related to increased vascular permeability of the ovarian tissues leading to fluid leaking into the abdomen and causing symptomatology. Large fluid shifts can lead to hypovolemic hyponatremia.

Patients may present with abdominal pain, nausea, vomiting, ascites, edema, dyspnea, electrolyte imbalances, and/or hypotension.

Symptoms depend on the degree of severity:

Mild cases occur when patients have some abdominal distention and pain. They often will have swelling, nausea, and vomiting as well. Ovarian size is usually smaller than 8 cm. This is thought to occur in up to 10% of patients.

Moderate cases have the same symptoms as mild cases plus ascites demonstrated on imaging studies.

Severe cases occur in about 1% of patients. Patients can have significant ascites as well as pleural effusions / respiratory distress, oliguria, electrolyte changes, thrombosis, and hemoconcentration. Ovarian size is usually larger than 12 cm.

Critical cases are rare but can be life-threatening, including arrythmia, thromboembolism, hydrothorax, pulmonary embolism, pericardial effusion, adult respiratory distress syndrome, renal failure, and/or sepsis.

Risk factors include ovarian stimulation undertaken at a young age, a history of prior OHSS, elevated antimullerian hormone levels, and a history of polycystic ovarian syndrome.