How should varicella infection be managed in a pregnant woman, including antiviral therapy, varicella‑zoster immune globulin, fetal monitoring, and neonatal prophylaxis?

Management of Chickenpox in Pregnancy

Pregnant women exposed to varicella who lack immunity should receive varicella-zoster immune globulin (VZIG) within 96 hours of exposure to prevent severe maternal complications, and if varicella develops despite prophylaxis, oral acyclovir 800 mg five times daily should be initiated within 24 hours of rash onset. 1

Initial Assessment of Exposed Pregnant Women

• Immediately obtain varicella-zoster IgG serology for any pregnant woman with possible varicella exposure, as patient history of disease is unreliable 1
• Immunity is confirmed by: documented two-dose varicella vaccination, laboratory-confirmed IgG positivity, or healthcare-provider-verified history of varicella or herpes zoster 1
• If serology is negative or results are unavailable within 96 hours, proceed immediately to VZIG administration 1

Post-Exposure Prophylaxis with VZIG

• Administer VZIG as soon as possible within 96 hours of exposure (ideally), though administration up to 10 days post-exposure provides some benefit 2, 1, 3
• Dosing: 125 units per 10 kg body weight, maximum 625 units, given intramuscularly 2, 4
• VZIG reduces varicella infection rates in exposed pregnant women from >70% to approximately 30% and markedly decreases severe outcomes such as pneumonia 1
• The primary purpose of VZIG is preventing severe maternal disease—it does NOT prevent viremia, fetal infection, or congenital varicella syndrome 2, 1

Critical Timing Considerations

• The 96-hour window is critical for maximal VZIG effectiveness, though some protection persists if given up to 10 days after exposure 1, 3
• VZIG may prolong the incubation period by up to one week, extending the monitoring period from 21 to 28 days 2, 1
• Recent data from 507 high-risk participants showed similar varicella incidence whether VZIG was given ≤96 hours versus >96 hours (up to 10 days): 6.2% versus 9.4% 3

Antiviral Treatment for Active Varicella in Pregnancy

• If varicella develops, initiate oral acyclovir 800 mg five times daily within 24 hours of rash onset 1
• Treatment is most effective when started within 24 hours; however, do not withhold treatment if this window is missed, especially in high-risk patients 1
• Acyclovir is FDA Pregnancy Category B with no increased birth defects documented in 596 first-trimester exposures 1
• Pregnant women are at higher risk for severe varicella and complications (particularly pneumonia) compared to non-pregnant adults 2, 1

Monitoring After VZIG Administration

• Observe closely for prodromal symptoms (fever, malaise, headache) followed by characteristic vesicular rash for 28 days after exposure if VZIG was given 2, 1
• If VZIG was not administered, monitor for 21 days 1
• Institute antiviral therapy immediately if any signs or symptoms of varicella develop 2

Fetal Monitoring Considerations

• VZIG does not prevent fetal infection or congenital varicella syndrome; its benefit is maternal 2, 1
• No specific fetal monitoring beyond routine obstetric care is indicated for maternal varicella exposure alone
• Congenital varicella syndrome risk is highest with maternal infection before 20 weeks gestation (general medical knowledge)

Neonatal Prophylaxis: Critical Peripartum Window

Highest-Risk Period

• The period from 5 days before delivery to 2 days after delivery represents the highest-risk window for neonatal varicella, with historical mortality rates of approximately 31% without intervention 5, 1
• This critical window occurs because the neonate lacks sufficient transplacentally acquired maternal antibody to protect against severe disease 5

Neonatal VZIG Administration

• Administer VZIG to all neonates born to mothers with varicella onset from 5 days before to 2 days after delivery, regardless of whether the mother received VZIG 2, 5, 1
• Neonatal dosing: 125 units per 10 kg body weight, maximum 625 units 5
• Administer as soon as possible after birth, ideally within 96 hours of exposure 5
• VZIG reduces complications and fatal outcomes substantially, though it does not prevent infection itself (attack rate remains approximately 62%) 5

Neonatal Antiviral Treatment

• If varicella develops despite VZIG prophylaxis, initiate intravenous acyclovir immediately 5
• Recommended neonatal dosing: 10 mg/kg IV infused over 1 hour, every 8 hours for 10 days 5
• Treatment is most effective when started within 24 hours of rash onset 5

Special Considerations for Premature Infants

Postnatal Exposure in Premature Infants

• Very premature infants (<28 weeks gestation or <1,000g) should receive VZIG after postnatal exposure regardless of maternal immunity status, as they may not have acquired sufficient maternal antibody 2, 5, 1
• Moderately premature infants (≥28 weeks gestation) should receive VZIG only if the mother lacks evidence of immunity 2, 5, 1
• Healthy full-term infants exposed postnatally do not require VZIG, even if mothers lack varicella history 2

Critical Pitfalls to Avoid

• Do not withhold neonatal VZIG even if the mother received VZIG, when maternal rash occurs 5 days before to 2 days after delivery 2, 5, 1
• Do not assume VZIG prevents infection—approximately 60% may still develop varicella, though severity and mortality are reduced 5
• Do not delay acyclovir if varicella develops—efficacy decreases significantly after 24 hours of rash onset 5, 1
• Do not delay obtaining serology or administering VZIG in exposed pregnant women; the 96-hour window is critical 1
• Do not administer live varicella vaccine during pregnancy—it is contraindicated, though inadvertent administration does not require pregnancy termination and has not been associated with congenital varicella syndrome 1

Breastfeeding Considerations

• Breastfeeding is not contraindicated in mothers with varicella, provided appropriate infection control measures are maintained (general medical knowledge)
• Ensure all lesions are crusted before close contact with the infant

Infection Control

• Implement airborne and contact precautions; patients are infectious from 2 days before rash onset until all lesions are completely crusted and dry 1
• Maintain isolation until all lesions are crusted 1