What is the appropriate evaluation and management of a rash in a pregnant woman?

Evaluation and Management of Rashes in Pregnant Women

The evaluation of a rash in pregnancy requires immediate differentiation between pregnancy-specific dermatoses and non-pregnancy conditions, with urgent laboratory assessment if intrahepatic cholestasis of pregnancy (ICP) or pemphigoid gestationis is suspected, as these carry significant fetal risks including stillbirth. 1, 2

Initial Clinical Assessment

Key Historical Features to Elicit

• Timing of onset: ICP typically presents after 30 weeks gestation (80% of cases), while atopic eruption of pregnancy (AEP) can occur at any trimester 1, 3
• Pruritus characteristics: Severe pruritus on palms and soles WITHOUT a primary rash suggests ICP, whereas pruritus with visible rash indicates other pregnancy dermatoses 1, 2
• Rash morphology and distribution: Eczematous lesions on face, neck, and flexural areas suggest AEP; urticarial papules and plaques on abdomen starting in third trimester indicate polymorphic eruption of pregnancy (PEP) 2, 4
• Presence of vesicles or bullae: These findings raise concern for pemphigoid gestationis, a rare but serious condition 2, 4

Critical Physical Examination Findings

• Blanching vs. non-blanching: Non-blanching petechiae or purpura indicate thrombocytopenic or vasculitic processes requiring immediate hematologic evaluation 2, 5
• Unilateral vs. bilateral distribution: Unilateral facial edema with erythema suggests cellulitis or allergic reaction rather than pregnancy-specific dermatosis 6
• Presence of excoriations: Severe scratching marks without primary lesions strongly suggest ICP 1, 3

Diagnostic Workup

For Pruritus With or Without Rash

Immediate laboratory testing should include: 1, 2

• Total serum bile acids (postprandial preferred): Levels ≥10 μmol/L confirm ICP; levels ≥100 μmol/L carry 3.4% risk of intrauterine fetal demise 1
• Liver function tests (AST, ALT): Elevations of 2-30 fold above normal support ICP diagnosis 1
• Repeat bile acid testing if initial results normal but pruritus persists: Laboratory abnormalities may lag behind symptoms 1

For Non-Blanching Rash (Petechiae/Purpura)

Urgent hematologic evaluation required: 2

• Complete blood count with differential and platelet count
• Peripheral blood smear
• Coagulation studies (PT/INR, aPTT)
• Comprehensive metabolic panel including liver function tests
• LDH and haptoglobin if hemolysis suspected
• Immediate referral to maternal-fetal medicine and hematology if platelets <100,000/μL 2

For Vesiculobullous Lesions

• Direct immunofluorescence of perilesional skin to diagnose pemphigoid gestationis 4
• This condition requires specialty referral due to fetal risks 3, 4

Management by Diagnosis

Intrahepatic Cholestasis of Pregnancy (ICP)

This is the highest-risk pregnancy dermatosis for the fetus. 1, 3

• Ursodeoxycholic acid (UDCA) is first-line therapy for symptom management and potential fetal benefit 1
• Lifestyle measures and antihistamines for pruritus control 1
• For refractory pruritus: rifampicin, cholestyramine, or SAMe may be added, though evidence of benefit is limited 1
• Monitor PT and administer vitamin K if elevated to prevent maternal postpartum hemorrhage and fetal intracranial hemorrhage (cholestyramine can exacerbate vitamin K deficiency) 1
• Fetal monitoring and consideration of early delivery, especially if bile acids ≥100 μmol/L 1
• Postpartum follow-up mandatory to confirm resolution and evaluate for underlying chronic liver disease 1

Atopic Eruption of Pregnancy (AEP)

This is the most common pregnancy dermatosis and carries no fetal risk. 7, 8, 4

First-line management: 5

• Regular application of emollients, especially after bathing, as foundation of therapy
• Moderate-potency topical corticosteroids on affected areas (avoid high-potency formulations on face)
• Loose, breathable clothing to reduce irritation

Antihistamine selection if needed: 5

• Chlorpheniramine is preferred due to long safety record
• Loratadine and cetirizine are FDA Pregnancy Category B alternatives
• Avoid hydroxyzine in first trimester (specifically contraindicated in early pregnancy)

Escalation if severe: 5, 9

• Prednisolone is the safest systemic corticosteroid (90% inactivated by placenta)
• Avoid betamethasone and dexamethasone (cross placenta more readily)
• Consider ultraviolet phototherapy for generalized disease 10, 8

Polymorphic Eruption of Pregnancy (PEP)

This condition typically presents in third trimester and carries no fetal risk. 2, 4

• Moderate-potency topical corticosteroids 11
• Oral antihistamines for pruritus (chlorpheniramine preferred) 5
• Symptoms typically resolve within weeks postpartum 7, 4

Pemphigoid Gestationis

This rare condition requires specialty referral due to fetal risks including prematurity. 2, 3, 4

• Systemic corticosteroids often necessary
• Close maternal-fetal medicine monitoring
• Increased surveillance for fetal complications

Cellulitis or Infectious Causes

For unilateral facial edema with erythema, warmth, and tenderness: 6

• Immediate antibiotic therapy with pregnancy-safe beta-lactams
• Dental evaluation if dental abscess suspected
• Assessment for airway involvement if angioedema considered

Critical Safety Considerations for Topical Corticosteroids

When prescribing topical corticosteroids in pregnancy: 11

• Use moderate-potency formulations; avoid very potent steroids
• Limit use over large surface areas and avoid prolonged application
• Do not use occlusive dressings (increases systemic absorption)
• Topical corticosteroids are Pregnancy Category C: use only if potential benefit justifies potential risk to fetus
• Monitor for HPA axis suppression if using potent steroids over large areas

Common Pitfalls to Avoid

• Do not dismiss pruritus without rash as "normal pregnancy symptom" – this may be ICP with serious fetal consequences 1, 3
• Do not delay bile acid testing if pruritus present – repeat testing if initially normal but symptoms persist 1
• Do not use systemic corticosteroids as first-line for AEP in first trimester – this is the critical period of organogenesis 5
• Do not assume all pregnancy rashes are benign – pemphigoid gestationis and ICP require urgent specialty referral 3, 4
• Do not prescribe hydroxyzine in early pregnancy – specifically contraindicated 5