What are the management and prevention strategies for a pregnant woman who is Hepatitis B surface antigen (HBsAg) positive?

Management of HBsAg-Positive Pregnancy

All HBsAg-positive pregnant women should have HBV DNA testing to guide antiviral therapy, and their infants must receive both hepatitis B vaccine and HBIG within 12 hours of birth to prevent perinatal transmission. 1

Maternal Testing and Monitoring

Initial Prenatal Testing

• Test all pregnant women for HBsAg during the first trimester of each pregnancy, regardless of prior vaccination or testing history 1
• Measure HBV DNA levels in all HBsAg-positive pregnant women to determine the need for antiviral prophylaxis 1
• Women not screened prenatally who are at high risk (injection drug use, multiple sex partners, STI history) should be tested at hospital admission for delivery 1

Antiviral Therapy During Pregnancy

• Initiate maternal antiviral therapy when HBV DNA exceeds 200,000 IU/mL to prevent perinatal transmission, as recommended by the American Association for the Study of Liver Diseases 1
• This threshold represents the point where vertical transmission risk becomes substantial despite standard infant immunoprophylaxis 2
• Tenofovir is the preferred antiviral agent and is safe during breastfeeding 3

Infant Prophylaxis Protocol

Immediate Postpartum Management (Within 12 Hours)

• Administer hepatitis B vaccine (single-antigen) AND HBIG (0.5 mL) within 12 hours of birth at separate injection sites 1, 4
• This combined regimen achieves 85-95% efficacy in preventing chronic HBV carrier state 4
• Efficacy decreases markedly if treatment is delayed beyond 48 hours 4

Special Considerations for Preterm Infants

• For infants weighing <2,000 g, do not count the birth dose toward the vaccine series due to reduced immunogenicity 1
• Administer 3 additional vaccine doses (total of 4 doses) beginning at 1 month of age 1

Vaccine Series Completion

• Complete the vaccine series at 1 month and 6 months after the first dose 1, 4
• Do not administer the final dose before 24 weeks (164 days) of age 1

Postvaccination Testing

Timing and Interpretation

• Test infants for anti-HBs and HBsAg at 9-18 months of age (typically at the next well-child visit) 1
• Do not test before 9 months to avoid detecting passively acquired anti-HBs from HBIG and to maximize detection of late infection 1
• Do not test for anti-HBc, as maternal antibodies may persist until 24 months of age 1

Response Categories

• Infants with anti-HBs >10 mIU/mL and HBsAg-negative are protected and require no further management 1
• Infants with anti-HBs <10 mIU/mL require additional evaluation and possible revaccination 1

Maternal Counseling and Case Management

Essential Information for HBsAg-Positive Mothers

• Refer all HBsAg-positive pregnant women to the Perinatal Hepatitis B Prevention Program for case management 1
• Provide written documentation of HBsAg status to the delivery hospital and the infant's healthcare provider 1

Counseling Topics

• Modes of HBV transmission and prevention strategies 1
• Breastfeeding is safe and should not be discouraged when proper infant immunoprophylaxis is provided 3, 1
• Breastfeeding safety applies even for mothers on tenofovir therapy 3
• Importance of hepatitis B vaccination for household contacts, sexual partners, and needle-sharing contacts 1
• Need for medical evaluation and possible treatment of chronic hepatitis B 1

Common Pitfalls to Avoid

Timing Errors

• The 12-hour window for infant immunoprophylaxis is critical—delays beyond 48 hours substantially reduce efficacy 4
• Do not delay breastfeeding initiation until after infant immunization, as transmission risk is minimal with proper prophylaxis 3

Testing Mistakes

• Do not skip HBV DNA testing in HBsAg-positive pregnant women, as this determines antiviral therapy necessity 1
• Avoid testing infants before 9 months, which can yield false results from passively acquired antibodies 1

Unnecessary Interventions

• Cesarean section is not indicated solely for HBV prevention when proper immunoprophylaxis is provided 5
• Bottle feeding is not necessary to prevent transmission when infants receive appropriate immunoprophylaxis 3, 5

Risk Stratification

High-Risk Mothers (HBeAg-Positive or High Viral Load)

• HBeAg-positive mothers have 80-90% transmission risk without intervention 6
• Maternal HBeAg can serve as a surrogate marker for high viral load (>200,000 IU/mL) with 95.5% sensitivity 2
• These mothers particularly benefit from third-trimester antiviral therapy 1, 7

Lower-Risk Mothers (HBeAg-Negative)

• Transmission risk is only 2-15% in HBeAg-negative mothers 6
• Standard infant immunoprophylaxis alone is typically sufficient 6, 7