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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Ovarian hyperstimulation syndrome

Obstetrics and gynaecology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
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Severe OHSS is a capillary-leak emergency

Rapid fluid shift can cause ascites, pleural effusion, haemoconcentration, renal impairment, respiratory compromise and venous or arterial thrombosis, sometimes at unusual sites.

Action: Assess airway, breathing, circulation, urine output and thrombosis symptoms; involve the fertility and gynaecology teams urgently, obtain severity investigations, admit when criteria are met and escalate organ dysfunction to critical care.

Synopsis

Prevent, recognise, grade and manage ovarian hyperstimulation syndrome using the 2026 RCOG classification, with early escalation for capillary leak, organ dysfunction and thrombosis.

  • OHSS is an iatrogenic increase in vascular permeability after ovarian stimulation, driven chiefly by hCG-related ovarian vasoactive mediators including VEGF.
  • Early OHSS follows the treatment trigger; late OHSS usually begins 10 days or more later and is sustained by endogenous hCG from pregnancy, often making it longer and more severe.
  • Mild disease has bloating or mild pain, ovaries usually below 8 cm and haematocrit below 0.40; moderate disease adds nausea or vomiting and ultrasound ascites, with ovaries usually 8 to 12 cm and haematocrit below 0.45.
  • Any severe feature defines severe disease: clinical ascites, haematocrit above 0.45, sodium below 135 mmol/L, potassium above 5 mmol/L, albumin below 35 g/L, serum osmolality below 282 mOsm/kg or oliguria below 300 mL/day or 30 mL/hour.
  • Critical OHSS includes tense ascites or pleural effusion, haematocrit above 0.55, white cells above 25 × 10^9/L, anuria, thromboembolism or ARDS.
  • Manage mild or moderate disease and selected stable severe disease as an outpatient only when pain and intake are controlled, follow-up is reliable and urgent advice is available; review stable outpatients every 2 to 3 days.
  • Avoid NSAIDs because renal perfusion is vulnerable. Use paracetamol and, when necessary, pregnancy-compatible opioids; prescribe LMWH thromboprophylaxis according to severity, pregnancy and individual risk.
  • Drain ascites under ultrasound guidance when it causes severe pain or distension, respiratory compromise or oliguria despite appropriate intravascular volume replacement.

Key red flags

Dyspnoea, hypoxia, chest pain, haemoptysis or a large pleural effusion may indicate respiratory compromise or pulmonary embolism.

Unilateral leg swelling, focal neurological deficit, severe headache, visual symptoms or neck swelling may represent venous or arterial thrombosis at a typical or unusual site.

Oliguria below 300 mL in 24 hours or below 30 mL/hour, anuria, rising creatinine or a positive fluid balance over 1 litre requires urgent review.

Tense or rapidly increasing ascites, severe pain, persistent vomiting, syncope, haemodynamic change or inability to maintain oral fluid intake supports admission.

Haematocrit above 0.55, white-cell count above 25 × 10^9/L, thromboembolism or acute respiratory distress syndrome meets critical-severity features.

Investigation priorities

01
Serial observations and fluid balanceFirst step

Detect respiratory, circulatory and renal deterioration.

Management branches

Immediate assessmentGrade severity and exclude mimics

Symptoms occur after ovulation induction or IVF stimulation.

  1. Record stimulation, trigger, retrieval, transfer and pregnancy timing; assess ABC, oxygen saturation, pain, vomiting, thrombosis symptoms, weight, girth and urine output.
  2. Obtain severity bloods and pelvic ultrasound, adding respiratory, thrombotic or acute-abdominal investigations from the presentation.
  3. Classify by the most severe feature, not by ovarian size alone, and contact the treating fertility unit early.
Outpatient careUse only when stability and access are reliable

Disease is mild or moderate, or selected severe disease is stable without an admission criterion.

  1. Confirm pain control, adequate oral intake and urine output, reliable transport and follow-up, and understanding of the 24-hour contact and deterioration symptoms.
  2. Use paracetamol or pregnancy-compatible opioid if required, avoid NSAIDs, assess VTE risk and prescribe stockings or LMWH when indicated.
  3. Review every 2 to 3 days while stable, sooner for any deterioration, repeating weight, girth, fluid balance and bloods according to severity.

Key medicines

Low-molecular-weight heparinUse the prophylactic LMWH dose specified by the local pregnancy and VTE protocol, adjusted for current weight and renal function; suspected or confirmed thrombosis requires a separate therapeutic regimen.Assess active bleeding, platelet history, renal impairment, planned procedures and neuraxial anaesthesia. Coordinate timing around paracentesis or surgery and distinguish prophylaxis from treatment.
ParacetamolGive 500 mg to 1 g orally every 4 to 6 hours as needed, maximum 4 g in 24 hours for a suitable adult; use a lower maximum for low body weight, hepatic risk or local policy.Check combination products, low body weight and liver disease. Avoid substituting NSAIDs because renal perfusion may be compromised, and reassess escalating or localised pain.
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Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • RCOG Green-top Guideline 5: management of OHSS, fourth edition
  • BJOG full guideline: management of OHSS
  • RCOG patient information on OHSS
  • NICE NG257 IVF procedures and OHSS prevention
  • ESHRE ovarian stimulation guideline update

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom