What are the diagnostic and management approaches for prenatal diagnosis of congenital varicella (chickenpox) in a pregnant woman?

Prenatal Diagnosis and Management of Congenital Varicella

Prenatal diagnosis of congenital varicella requires serologic testing, ultrasound examination, and possibly invasive procedures like amniocentesis, with management focused on timing of maternal infection due to the highest risk (2%) occurring between 13-20 weeks gestation. 1, 2

Diagnostic Approach

Maternal Infection Assessment

• Diagnosis of maternal varicella infection is primarily clinical, based on characteristic vesicular rash 1
• Confirm maternal infection through serologic testing for varicella-specific IgM and IgG antibodies 3
• Document timing of maternal infection, as risk of congenital varicella syndrome varies significantly by gestational age 1

Fetal Assessment

• Perform detailed ultrasound examination 2-4 weeks after maternal infection to evaluate for structural abnormalities 3
• Look for specific ultrasound findings associated with congenital varicella syndrome:
  • Limb hypoplasia
  • Microcephaly
  • Cortical atrophy
  • Hydrocephaly
  • Intrauterine growth restriction 1, 4

Invasive Diagnostic Procedures

• Consider amniocentesis for detection of VZV DNA by PCR, particularly for infections occurring between 7-20 weeks gestation 5, 4
• PCR testing of amniotic fluid has been shown to detect VZV DNA in affected fetuses 5
• Fetal blood sampling may be used to detect VZV-specific IgM antibodies, though sensitivity is limited 4
• Dot blot hybridization using radiolabelled DNA probes can confirm positive PCR results 4

Risk Assessment by Gestational Age

First Trimester (0-12 weeks)

• Risk of congenital varicella syndrome is approximately 0.4% (95% CI: 0.05-1.5%) 1, 2
• Lower risk compared to second trimester but still warrants close monitoring 1

Second Trimester (13-20 weeks)

• Highest risk period with approximately 2.0% risk (95% CI: 0.8-4.1%) of congenital varicella syndrome 1, 2
• Most reported cases of congenital varicella syndrome occur after maternal infection during this period 6

Late Second and Third Trimester (>20 weeks)

• Risk decreases significantly after 20 weeks gestation 1
• Isolated cases have been reported with the latest occurring at 28 weeks gestation 1
• No cases reported after 28 weeks in large prospective studies 1

Peripartum Period (5 days before to 2 days after delivery)

• High risk (17-30%) of severe neonatal varicella infection 1
• Significant risk of neonatal mortality without intervention 1

Management Strategies

Maternal Management

• For susceptible pregnant women exposed to varicella, administer varicella-zoster immune globulin (VZIG) as post-exposure prophylaxis 1, 7
• VZIG may reduce risk of maternal infection but has not been proven to prevent fetal infection 6
• For pregnant women with active varicella infection, consider antiviral therapy (acyclovir) particularly for severe disease 7

Fetal Surveillance

• Schedule serial ultrasound examinations every 2-4 weeks following maternal infection to monitor for development of congenital abnormalities 3
• If abnormalities are detected, counsel regarding prognosis and management options 3
• In cases of confirmed fetal infection with significant abnormalities, pregnancy termination may be discussed as an option, particularly during high-risk periods 5

Neonatal Management

• For peripartum maternal infection (5 days before to 2 days after delivery), administer VZIG to the newborn immediately after birth 1
• VZIG has been reported to reduce the incidence of severe neonatal varicella 1
• Test infant serum for varicella-specific antibodies 3
• Perform comprehensive clinical evaluation of infants born to mothers with confirmed varicella during pregnancy 3

Prevention

• Screen women of childbearing age for varicella immunity before pregnancy 7
• Vaccinate non-pregnant seronegative women of childbearing age 7
• Avoid vaccination during pregnancy 7
• Counsel pregnant women to avoid exposure to individuals with active varicella or zoster 3

Prognosis

• Approximately 30% of infants born with congenital varicella syndrome die in the first months of life 6
• Survivors may have significant long-term morbidity related to neurological, ophthalmological, and musculoskeletal abnormalities 6
• Herpes zoster may develop during infancy or early childhood in approximately 0.8-1.7% of infants exposed to VZV in utero during 13-36 weeks gestation 1