What is the appropriate assessment and management of ovarian hyperstimulation syndrome (OHSS) in a pre‑menopausal woman undergoing controlled ovarian stimulation?

Ovarian Hyperstimulation Syndrome: Assessment and Management

For women undergoing controlled ovarian stimulation who develop severe OHSS, initiate prophylactic anticoagulation with LMWH (enoxaparin 40 mg daily) for 3 months post-resolution of clinical symptoms, combined with supportive outpatient management including paracentesis for symptomatic ascites. 1

Clinical Recognition and Severity Classification

OHSS manifests as a capillary leak syndrome with pleural effusion, ascites, and in severe cases, arterial/venous thrombosis and renal failure 2. Classify severity immediately upon diagnosis as mild, moderate, severe, or critical to guide management intensity 3.

Key Clinical Features to Assess:

• Ascites severity (tense ascites requires intervention)
• Hematocrit and renal function (hemoconcentration indicates severity)
• Respiratory compromise (pleural effusions)
• Thromboembolic risk factors (underlying thrombophilia dramatically increases risk)

Thromboprophylaxis: The Critical Intervention

The most life-threatening complication of OHSS is venous thromboembolism, with underlying thrombophilia substantially increasing the risk of severe OHSS 2. The evidence strongly supports anticoagulation:

Standard Approach:

• Enoxaparin 40 mg subcutaneously daily starting when severe OHSS is diagnosed 2
• Withhold 24-36 hours prior to any oocyte retrieval, resume afterward 2
• Continue for 3 months post-resolution of clinical OHSS 1
• If pregnancy occurs, continue throughout pregnancy and postpartum period 2

Special Populations Requiring Therapeutic Anticoagulation:

• Women with thrombotic APS: Use therapeutic-dose LMWH (enoxaparin 1 mg/kg subcutaneously every 12 hours) 2
• Women with known thrombophilia: Thromboprophylaxis is recommended to prevent thrombotic complications of moderate-to-severe OHSS 2

The rationale is compelling: In women with severe OHSS, prophylactic LMWH reduces VTE risk by 26 fewer events per 1,000 women (from baseline risk of 40/1,000 to 14/1,000), with no significant increase in major bleeding 1. The number needed to treat is only 39 1.

Outpatient vs. Inpatient Management

Mild and moderate OHSS should be managed as outpatients 3. For severe OHSS, outpatient management is safe and cost-effective if the patient can adhere to instructions and assessment occurs every 1-2 days 4, 3.

Outpatient Management Protocol:

• Daily weight and abdominal girth measurements
• Fluid balance monitoring (intake/output)
• Assessment every 1-2 days for disease progression
• Outpatient paracentesis/culdocentesis for moderate-to-severe cases to prevent progression 3

Hospitalization Criteria (Severe/Critical OHSS):

• Inability to maintain adequate oral hydration
• Severe hemoconcentration despite outpatient management
• Renal dysfunction
• Respiratory compromise
• Tense ascites requiring drainage 3

Supportive Management

Fluid Management:

• Initiate IV crystalloid solution to prevent hemoconcentration and maintain end-organ perfusion 3
• If crystalloid fails to maintain perfusion, switch to colloid solution 3
• Monitor for fluid overload while preventing hypovolemia

Paracentesis:

• Perform paracentesis for tense ascites in admitted patients for symptomatic relief 3
• Consider outpatient culdocentesis for moderate/severe OHSS to prevent disease progression 3
• Paracentesis is effective treatment along with supportive management 4

Pain Management:

• Acetaminophen and/or opioid analgesics 3
• Avoid NSAIDs with antiplatelet properties (increases bleeding risk, particularly problematic given anticoagulation) 3

Critical OHSS: Multidisciplinary Approach

Critical OHSS requires hospitalization and management by a multidisciplinary team according to the end organ affected 3. This includes:

• Intensive care monitoring
• Nephrology consultation for renal failure
• Pulmonary consultation for respiratory compromise
• Hematology for thrombotic complications

Prevention Strategies During Stimulation

While this question focuses on management, prevention protocols that yield lower peak estrogen levels (such as those incorporating aromatase inhibitors) benefit patients at risk for OHSS 2. When more than 2 dominant follicles >15mm or >5 follicles >10mm are present, IUI should be withheld to prevent complications 5.

Common Pitfalls to Avoid

1. Discontinuing anticoagulation prematurely: In one series, 2 of 4 thromboses occurred in women who discontinued LMWH after oocyte retrieval 2
2. Using aspirin before oocyte retrieval: Avoid due to prolonged antiplatelet action increasing bleeding risk at retrieval 2
3. Underestimating thrombotic risk: Most VTE events occur days to weeks (range 2 days-11 weeks) after OHSS resolution 1
4. Delaying paracentesis: Early drainage prevents progression and provides symptomatic relief 4, 3

For routine assisted reproduction without OHSS, thromboprophylaxis is NOT recommended (Grade 1B) 1, as the baseline VTE risk is only 2/1,000, making the number needed to treat 781 1.