In a 37‑week pregnant woman exposed to varicella but without a rash, should she be concerned and what is the appropriate management?

Management of Varicella Exposure at 37 Weeks Gestation

If you have no history of chickenpox or vaccination, you should be very concerned and need immediate action within 96 hours—specifically, you need urgent varicella immunity testing and likely varicella-zoster immune globulin (VZIG) if you are non-immune. 1

Immediate Assessment Required

Your first step is determining your immunity status:

• If you have a documented history of chickenpox or varicella vaccination, you are immune and require no intervention whatsoever 2
• If you have no history or uncertain history, you need immediate serologic testing for varicella antibodies 1, 3
• The critical window is 96 hours from exposure—VZIG effectiveness diminishes significantly after this timeframe 1

Why This Matters at 37 Weeks

At 37 weeks gestation, you face two distinct risks if you are non-immune and develop chickenpox:

Maternal Risk

• Pregnant women are at significantly higher risk for severe varicella complications, particularly pneumonia, compared to non-pregnant adults 1, 3
• Varicella pneumonitis can be life-threatening and requires hospitalization with intravenous acyclovir 3, 4

Neonatal Risk (The Critical Concern at Your Gestational Age)

• The highest-risk period is when maternal rash appears between 5 days before delivery and 2 days after delivery 1, 5
• Neonates born during this window face severe, potentially fatal disseminated varicella 1, 5
• Your baby would require immediate VZIG administration at birth regardless of whether you received VZIG during pregnancy 1, 3

What You Need to Do Now

Within 96 Hours of Exposure:

If you are non-immune or immunity status is unknown:

• Receive VZIG immediately—this prevents severe maternal complications 1, 2
• VZIG does NOT prevent fetal infection or viremia, but it protects you from severe disease 1
• If VZIG is unavailable or the 96-hour window has passed, oral acyclovir prophylaxis can be considered 1

Extended Monitoring Period:

• If you receive VZIG, you must be monitored for 28 days (not the usual 21 days) for signs of varicella because VZIG prolongs the incubation period 1
• Watch for any rash development during this extended period 1

If You Develop Chickenpox

Treatment must begin within 24 hours of rash onset:

• Oral acyclovir 800 mg five times daily should be started immediately 1, 3
• This reduces severity of maternal symptoms but does not prevent fetal transmission 1
• If you develop respiratory symptoms suggesting pneumonitis, immediate hospitalization with intravenous acyclovir (10-15 mg/kg every 8 hours) is required 3

Neonatal Management:

• Alert your obstetric team and neonatal providers immediately 3
• Your newborn will require VZIG administration at birth 1, 5
• The baby will need close monitoring and potentially acyclovir treatment 5

Important Caveats

Common pitfall to avoid: Failing to act within the 96-hour window for VZIG administration is the most critical error in managing varicella exposure during pregnancy 1

Reassuring note on fetal malformations: At 37 weeks, congenital varicella syndrome is not a concern—this only occurs with first or second trimester infection (risk 0.4-2.0%) 6, 7, 4. Your concern is neonatal varicella, not congenital malformations.

If you are immune: Approximately 95.5-99.6% of adults have immunity by age 20-40 years 2. If you had chickenpox as a child or were vaccinated, you can be reassured that no intervention is needed 2.