What is the appropriate management for a rash in a 20-week pregnant patient?

Management of Rash in a 20-Week Pregnant Patient

The appropriate management begins with identifying whether this is a pregnancy-specific dermatosis versus a non-pregnancy condition, with particular urgency to rule out intrahepatic cholestasis of pregnancy (ICP) and pemphigoid gestationis, as these pose fetal risks including prematurity and stillbirth. 1, 2

Immediate Diagnostic Priorities

First, determine if pruritus exists without a rash, as this is the hallmark presentation of ICP, which carries significant fetal risks including stillbirth and requires immediate laboratory evaluation with liver function tests and bile acids. 3, 1, 2

If a rash is present, assess the following specific characteristics:

• Timing of onset: Third trimester onset suggests polymorphic eruption of pregnancy (PEP/PUPPP), though it can occur at 20 weeks; first or second trimester onset may indicate pemphigoid gestationis or atopic eruption. 2
• Location: Rash starting in abdominal striae and sparing the umbilicus suggests PEP; palms and soles pruritus without rash indicates ICP; widespread distribution may indicate pemphigoid gestationis or atopic eruption. 1, 2
• Morphology: Urticarial papules and plaques suggest PEP; vesicles and bullae indicate pemphigoid gestationis; eczematous changes suggest atopic eruption. 2

Pregnancy-Specific Dermatoses Classification

The four main pregnancy-specific dermatoses are:

• Polymorphic eruption of pregnancy (PEP): Most common, benign to fetus, distressing only to mother. 1, 2
• Pemphigoid gestationis: Rare, associated with prematurity and small-for-date babies, requires immunofluorescence confirmation. 1, 2
• Intrahepatic cholestasis of pregnancy (ICP): Pruritus without primary rash, poses increased risk for fetal distress, prematurity, and stillbirth. 1, 2
• Atopic eruption of pregnancy: Most common overall dermatosis in pregnancy, benign to fetus. 2, 4

First-Line Treatment for Benign Pregnancy Dermatoses

For PEP and atopic eruptions (which pose no fetal risk), initiate conservative management immediately:

• Apply emollients regularly, especially after bathing, as the foundation of therapy to maintain skin barrier function and reduce inflammation. 5, 6
• Recommend loose, breathable clothing made from natural fabrics to reduce friction and irritation. 5, 6
• Maintain skin dryness in affected areas to prevent secondary infection and reduce inflammation. 5, 6

Pharmacologic Management When Conservative Measures Fail

Use moderate-potency topical corticosteroids as second-line therapy, avoiding very potent formulations initially and avoiding prolonged use of high-potency preparations throughout pregnancy. 5, 6

For severe pruritus requiring antihistamines:

• Chlorphenamine is the preferred antihistamine due to its long safety record in pregnancy, though all antihistamines should ideally be avoided in the first trimester. 3
• Cetirizine is FDA Pregnancy Category B and may be used if necessary, using the lowest effective dose. 3
• Avoid hydroxyzine, which is specifically contraindicated in early pregnancy. 3

Systemic Corticosteroids for Severe Cases

If systemic corticosteroids become necessary (rare for PEP, more common for pemphigoid gestationis), prednisolone is the only safe choice because it is 90% inactivated by the placenta. 5

• Never use betamethasone or dexamethasone, as they cross the placenta readily and could affect the fetus. 5
• Systemic corticosteroids control pemphigoid gestationis, PEP, and atopic eruptions effectively. 2

Special Considerations for Secondary Fungal Infection

If intertrigo or candidal infection is suspected in skin folds:

• Use topical nystatin (100,000 units/ml suspension or 200,000 units pastilles) as the first-line antifungal. 6, 3
• Avoid systemic azole antifungals entirely in the first trimester due to teratogenic potential. 5, 6
• Local azole preparations may be used cautiously after the first trimester if necessary, but nystatin remains preferred. 6

Critical Pitfalls to Avoid

• Never dismiss pruritus without rash as "just pregnancy" – always evaluate for ICP with laboratory testing, as it carries significant fetal mortality risk. 3, 1, 2
• Do not start with very potent topical corticosteroids – moderate potency is sufficient and safer. 5
• Do not use systemic azoles in the first trimester – use topical nystatin instead. 5
• Remember that pregnancy dermatoses can present postpartum, so maintain diagnostic vigilance even after delivery. 7