Ovarian hyperstimulation syndrome (OHSS)

Definition

• Ovarian hyperstimulation syndrome is a potentially life-threatening iatrogenic complication of ovarian stimulation in which the ovaries become markedly swollen and fluid leaks into the abdomen and chest.

Classification

• Mild, moderate, severe and critical forms are distinguished; the mild form with enlarged ovaries, abdominal bloating and mild abdominal pain is the most frequent.
• Severe forms show clinical ascites with or without hydrothorax, hyperkalaemia, hyponatraemia, oliguria and haemoconcentration with a haematocrit above 45%; critical forms involve a haematocrit above 55%, oliguria or anuria, thromboembolic events or acute respiratory distress syndrome.

Occurrence & epidemiology

Epidemiology

• OHSS affects about 3–6% of women undergoing assisted reproduction; after gonadotrophin stimulation, figures of 10–20% are also reported depending on source and definition, and severe courses are rare.

Aetiopathogenesis

Aetiology and pathogenesis

• It usually follows stimulation with gonadotrophins and is rare after oral stimulation alone; hCG used to trigger ovulation and pregnancy in the same cycle increase the risk.
• hCG promotes ovarian production of VEGF, which increases capillary permeability; intravascular volume shifts into the extravascular space with ascites, haemoconcentration and hypovolaemia, and severity correlates with VEGF levels.
• Risk factors include age under 35, polycystic ovary syndrome, low body weight, very high oestrogen levels and an unusually large number of follicles.

Clinical features

• Mild forms show abdominal bloating, mild abdominal pain and weight gain; severe forms present with severe abdominal pain, abdominal swelling, rapid weight gain, shortness of breath, nausea, vomiting and reduced urine output.
• Life-threatening complications include thromboembolic events, acute kidney failure, acute respiratory distress syndrome and severe electrolyte disturbances; ovarian torsion may also occur.

Diagnosis

• Laboratory findings include haemoconcentration with a raised haematocrit, leucocytosis, hyponatraemia, hyperkalaemia, raised creatinine and signs of liver dysfunction.
• Abdominal or transvaginal ultrasound and chest X-ray demonstrate enlarged ovaries, ascites and pleural effusions.

Keep learning in the app

Further reading (selection)

1. MedlinePlus Medical Encyclopedia: Ovarian hyperstimulation syndrome (U.S. National Library of Medicine)
2. Ovarian Hyperstimulation Syndrome (OHSS): A Narrative Review and Legal Implications (J Pers Med 2024, PubMed Central)
3. MSD Manual Professional: Ovulatory Dysfunction

Cross-references