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Advanced Fertility guide

Ovarian Hyperstimulation Syndrome (OHSS)

Recognising OHSS after fertility treatment, understanding prevention strategies and knowing when hospital care is needed.

Specialist-depth overview
10–12 min readUpdated 21 July 2026Evidence-informed patient education

Ovarian hyperstimulation syndrome is a potentially serious complication of ovarian stimulation, particularly during IVF. Mild discomfort is common after egg collection, but increasing swelling, vomiting, reduced urine or breathlessness needs prompt contact with the fertility unit.

OHSS can worsen after a positive pregnancy test and may evolve over several days.
Prevention begins during stimulation through dose selection, monitoring and trigger or embryo-transfer strategy.
Severe symptoms require specialist assessment because fluid balance, clot risk and organ function can be affected.
Original educational diagram for Ovarian Hyperstimulation Syndrome (OHSS)
Original educational diagram created for this topic. It explains the care pathway visually and is not a diagnostic image.

Risk and prevention

Higher ovarian reserve, PCOS, a large follicle response and previous OHSS can increase risk. Clinicians may adjust medication, use a different trigger, freeze all embryos or prescribe additional prevention according to the treatment protocol.

Symptoms and severity

Mild bloating and discomfort can occur after egg collection. Concerning features include rapidly increasing abdominal size, persistent vomiting, inability to drink, reduced urine, chest symptoms, severe pain or marked weight gain over a short period.

Assessment and treatment

The fertility unit assesses observations, abdominal findings, urine output, blood concentration, electrolytes, kidney and liver function and ultrasound findings. Treatment ranges from outpatient monitoring to hospital care, fluid management, drainage or thrombosis prevention.

Pregnancy and follow-up

If pregnancy occurs, symptoms can last longer because pregnancy hormones stimulate the ovaries. Follow-up continues until symptoms and blood tests resolve. The experience should inform any future stimulation protocol.

Questions worth discussing at your consultation

  • What is my individual OHSS risk?
  • Which prevention strategy is included in my protocol?
  • What daily symptoms or measurements should I track?
  • Who should I contact outside clinic hours?
When to seek urgent careContact the fertility unit or emergency service urgently for breathlessness, chest pain, fainting, severe abdominal pain, very little urine, persistent vomiting, a swollen painful leg or rapidly worsening abdominal swelling.
Medical note: This page is educational and is structured to support a specialist consultation. Diagnosis, investigations and treatment must be individualised. It has not been presented as a substitute for an examination or emergency assessment.