Maternal Antiviral Prophylaxis to Prevent Perinatal Transmission of Hepatitis B Virus in Thailand

Inclusion Criteria: * Pregnancy * At least 18 years of age * Negative Human Immunodeficiency Virus (HIV) serology * Positive HBsAg and hepatitis B e antigen (HBeAg) tests * Gestational age of 28 weeks (+ or - 10 days) as determined by obstetrician * Alanine Aminotransferase (ALT)≤30 U/L, confirmed ≤60 U/L on a subsequent blood draw * Agreeing to bring their infants at the planned study visits at one study site until one year after delivery and to inform the site investigators if they plan to move to another place and not be able to return to the clinic. * Understanding the need for adequate infant immunization and agreeing to the blood draws from their infants and the need for close follow up to manage possible exacerbation of hepatitis. Exclusion Criteria: * History of tenofovir treatment at any time, or any other anti-HBV treatment during the current pregnancy * Creatinine clearance \<50 ml/min, calculated using the Cockcroft-Gault formula * Dipstick proteinuria\>1+ (\>30 mg/dL) or normoglycemic glucosuria confirmed on two separate occasions * Positive serology for Hepatitis C infection less than 12 months prior to enrollment * Evidence of pre-existing fetal anomalies incompatible with life * Any concomitant condition or treatment that, in the view of the clinical site investigator, would contraindicate participation or satisfactory follow up in the study. * Concurrent participation in any other clinical trial without written agreement of the two study teams