The Management of Ovarian Hyperstimulation Syndrome Green-top Guideline No. 5 February 2016; SUMMARY

🩺 Ovarian Hyperstimulation Syndrome (OHSS) 

📌 What is OHSS?

OHSS is a complication of fertility treatment caused by pharmacological ovarian stimulation to increase the number of oocytes for assisted reproductive technology (ART).

🔬 Pathophysiology of OHSS

OHSS primarily occurs due to exposure of hyperstimulated ovaries to human chorionic gonadotropin (hCG) or luteinizing hormone (LH) after controlled ovarian stimulation with follicle-stimulating hormone (FSH).

Exposure of hyperstimulated ovaries leads to:

✅ Increased vascular permeability
✅ Prothrombotic effects
✅ Fluid loss into third spaces (ascites, pleural, or pericardial effusions)
✅ Severe hypovolemia (up to 20% blood volume loss)
✅ Hypo-osmolality and hyponatremia (due to altered osmotic thresholds)

📉 Incidence of OHSS

• True incidence is unknown due to a lack of mandatory reporting for mild/moderate cases.
• Reported OHSS incidence in IVF cycles:
  • Mild OHSS – Affects up to one-third of cycles
  • Moderate/Severe OHSS – Incidence ranges from 3.1% to 8%
  • Hospitalization due to OHSS – 0.3% (Europe) and 1.1% (USA)

⚠️ High-Risk Groups

Women at higher risk of OHSS include those with:
🔹 Polycystic ovary syndrome (PCOS)
🔹 High antral follicle count (AFC)
🔹 Elevated Anti-Müllerian Hormone (AMH) levels
🔹 Conceived cycles (due to endogenous hCG stimulation)
🔹 Multiple pregnancies (highest risk)

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🩺 Diagnosis of OHSS / INVESTIGATIONS / CATEGORY

📍 Clinical Diagnosis

OHSS is diagnosed clinically as there is no specific diagnostic test.

🔎 Symptoms of OHSS:
✅ Abdominal bloating and discomfort
✅ Nausea, vomiting
✅ Breathlessness, reduced urine output
✅ Leg and vulval swelling
✅ Signs of dehydration and tachycardia

📍 Early vs. Late OHSS

🟢 Early OHSS – Develops within 7 days of hCG trigger, usually due to excessive ovarian response.
🔴 Late OHSS – Develops 10+ days after hCG trigger, often due to pregnancy-related hCG stimulation (tends to be more prolonged and severe).

Examination and investigation of women with suspected OHSS

How is the severity of OHSS classified? 
The severity of OHSS should be graded according to a standardised classification scheme.

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🏡 Outpatient Management of OHSS

✅ Suitable for mild to moderate OHSS (selected severe cases).
✅ Patient education on fluid intake and output monitoring is essential.
❌ Avoid NSAIDs to protect renal function.
✅ Severe OHSS patients should receive thromboprophylaxis with LMWH.
✅ Paracentesis (fluid drainage) may be performed on an outpatient basis under ultrasound guidance.

• Women with OHSS being managed on an outpatient basis should be reviewed urgently if they develop symptoms or signs of worsening OHSS 
• In the absence of these, review every 2–3 days is likely to be adequate. 
• Baseline laboratory investigations should be repeated if the severity of OHSS is thought to be worsening.
•  Haematocrit is a useful guide to the degree of intravascular volume depletion.   

🏨 Inpatient Management of OHSS

🏨 Hospital Admission Criteria for OHSS

Hospital admission should be considered for women who:

❌ Have uncontrolled pain that cannot be managed with standard pain relief
❌ Are unable to maintain adequate fluid intake due to severe nausea or vomiting
❌ Show signs of worsening OHSS despite outpatient management
❌ Cannot attend regular outpatient follow-ups for monitoring
❌ Develop critical OHSS

👩‍⚕️ Multidisciplinary Care for Severe OHSS

✅ Severe and critical OHSS cases require a team of specialists, especially if dehydration and hemoconcentration persist.
✅ Intensive care may be needed for critical OHSS.
✅ A clinician experienced in OHSS should lead the patient's treatment.

📊 Monitoring Women Admitted with OHSS

Regular assessments and lab monitoring are essential to track progression and prevent complications.

✅ Daily Assessments (More Frequent for Critical OHSS)

• 🩺 Vital signs: Blood pressure, heart rate, respiratory rate, temperature
• ⚖️ Weight and abdominal girth measurement
• 💧 Fluid balance: Monitor intake/output to detect worsening OHSS

🩺 Laboratory Tests

🔬 Routine Tests:

• 🩸 Full blood count (FBC): Check for hemoconcentration and leukocytosis
• 🔴 Hematocrit (>0.45): Indicates worsening OHSS
• 💦 Serum electrolytes & osmolality: Assess dehydration and sodium balance
• 🏥 Liver function tests (LFTs): Monitor hypoalbuminemia

🔎 Additional Tests (If Needed):

• 🫁 Arterial blood gases (ABGs): Check oxygenation and acid-base balance
• ❤️ ECG: Detect cardiac strain from fluid shifts
• 📸 Chest X-ray: Identify pleural effusion or pulmonary issues

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📌 Signs of Worsening OHSS 🚨

🔺 Increasing abdominal girth and weight gain
🔺 Oliguria (low urine output) with positive fluid balance
🔺 Elevated hematocrit (>0.45), indicating dehydration

📌 Indicators of Recovery ✔️

💦 Increased urine output (diuresis)
🩸 Normalized hematocrit
⚖️ Reduced abdominal girth and weight

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✅💊 Symptom Relief in OHSS

✅ Pain Management:

• 💊 Paracetamol and opioids (if required)
• ❌ Avoid NSAIDs due to the risk of renal impairment

✅ Antiemetics for Nausea/Vomiting:

• ✅ Safe options: Metoclopramide and ondansetron

✅ Fluid Management

✅ Oral hydration is preferred (guided by thirst).
✅ IV colloids for severe dehydration may be considered.
❌ Diuretics should be avoided, except in multidisciplinary settings (if oliguria persists despite fluid resuscitation and paracentesis).

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✅ Thromboprophylaxis (Preventing Blood Clots)

✅ LMWH prophylaxis for severe/critical OHSS
✅ Women with moderate OHSS should be evaluated for predisposing risk factors for thrombosis and prescribed either antiembolism stockings or LMWH if indicated.
✅ Extended thromboprophylaxis may be required if pregnancy occurs

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✅ Paracentesis for Ascites (Fluid Drainage)

🔎 Indications for paracentesis:
✔️ Severe abdominal pain/distension
✔️ Respiratory compromise
✔️ Oliguria (low urine output) despite fluid resuscitation
✅ Ultrasound-guided drainage is recommended to minimize risks.

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✅ Surgical Indications

Surgery is only indicated in cases of if there is a coincident problem such as:

✔️ Adnexal torsion
✔️ Ovarian rupture
✔️ Ectopic pregnancy

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🤰 OHSS and Pregnancy

🔹 Pregnancies complicated by OHSS are at increased risk for:
✅ Pre-eclampsia
✅ Preterm delivery

❌ No significant increase in miscarriage risk, but there may be a higher rate of preclinical pregnancy loss in early OHSS cases.

SO;

📑 Reporting and Organising Care for OHSS

📌 How Should OHSS Be Reported?

✅ Licensed fertility centres must comply with Human Fertilisation and Embryology Authority (HFEA) regulations to report severe or critical OHSS cases.
✅ Units treating OHSS patients should inform the licensed centre where the fertility treatment was conducted to ensure clinical continuity and legal compliance.

🏥 Organisation of Services

📢 How Should Care Be Delivered for Women at Risk of OHSS?

✅ Fertility clinics should provide verbal and written information about OHSS to all women undergoing treatment.
✅ Women should receive a 24-hour contact number for emergencies.
✅ Acute care units must develop local protocols for OHSS assessment and management.
✅ Hospitals should ensure access to experienced clinicians skilled in OHSS management.
✅ Licensed fertility centres should maintain close coordination with acute units where their patients may present.