Causes of Eosinophilia in Pregnancy
Eosinophilia in pregnancy has the same underlying causes as in non-pregnant individuals, with allergic/atopic disorders accounting for approximately 80% of cases, followed by parasitic helminth infections as the second most common cause. 1
Primary Causes by Category
Allergic and Atopic Disorders (Most Common)
- Allergic/atopic conditions constitute 80% of secondary reactive eosinophilia cases, including asthma, food allergies, atopic dermatitis, and drug reactions 1, 2
- Drug-induced eosinophilia from medications such as non-steroidal anti-inflammatory drugs, beta-lactam antibiotics, and nitrofurantoin 1, 2
Parasitic Infections (Second Most Common)
- Helminth infections are the most common identifiable infectious cause, with diagnosis rates of 19-80% in travelers and migrants 2
- Strongyloides stercoralis (can persist lifelong and cause hyperinfection syndrome) 2
- Hookworm (Ancylostoma duodenale, Necator americanus) 1, 2
- Ascaris lumbricoides 1, 2
- Schistosomiasis (particularly with freshwater exposure in Africa) 1, 2
- Filariasis (especially with travel to West Africa) 1, 2
- Toxocariasis 2
Hematological and Neoplastic Causes
- Myeloid and lymphoid neoplasias with eosinophilia and tyrosine kinase fusion genes 1
- Solid tumors, especially in advanced disease 1
Autoimmune and Connective Tissue Disorders
- Eosinophilic fasciitis (rare, characterized by pain, swelling, and induration of extremities with peripheral eosinophilia) 3
- Other autoimmune diseases 1, 4
Pregnancy-Specific Rare Conditions
- Pregnancy-associated hypereosinophilia with hyperpermeability syndrome (extremely rare, life-threatening condition presenting with pericardial effusion, pleural effusion, and ascites) 5
- Cyclic angioedema with eosinophilia (rare, characterized by recurrent eosinophilia with edema and fever, responsive to prednisone) 6
Critical Diagnostic Considerations
Travel and Exposure History
- Geographic area visited is crucial for narrowing differential diagnosis, as helminth distribution varies by region 2
- Timing of exposure matters: eosinophilia may be transient during tissue migration phase when stool microscopy is negative 1, 2
- Serological tests may not become positive until 4-12 weeks after infection 1
Clinical Pitfalls to Avoid
- Many helminth infections do not cause eosinophilia, so absence of eosinophilia does not exclude parasitic infection 2
- Serological tests exhibit cross-reactivity between different helminth species 2
- Persistent eosinophilia >1.5 × 10⁹/L can cause significant end-organ damage to heart, lungs, central nervous system, and skin even without identifiable cause 1, 2
Urgent Assessment Indicators
- Patients with eosinophilia and evidence of end-organ damage (dyspnea, pericardial/pleural effusion, neurological symptoms) need urgent medical assessment 2, 5
- High-grade prolonged eosinophilia (>1.5 × 10⁹/L) requires prompt evaluation for potential complications 1
Diagnostic Workup Priorities
Initial Testing
- Detailed medication history and assessment for allergic conditions 1, 2
- Travel history with specific geographic locations and freshwater exposures 2
- Concentrated stool microscopy or alternative tests for all patients 7
- Strongyloides serology (high diagnostic yield across all regions) 7
Specialized Testing Based on Exposure
- Schistosomiasis serology if freshwater exposure in endemic areas 7, 2
- Filariasis testing if travel to West Africa 1, 2
- HIV testing per guidelines (HIV associated with eosinophilia, though helminth co-infection more likely) 7
Referral Indications
- Persistent eosinophilia ≥1.5 × 10⁹/L for more than 3 months with no identified cause warrants hematology referral 2