Mother-to-child transmission (MTCT) of hepatitis B virus (HBV) remains the major mode of transmission in most high and intermediate HBV endemic areas, despite existing WHO immunoprophylaxis recommendations. This immunoprophylaxis regimen, if given optimally, can prevent 75-80% of HBV MTCT, but optimal implementation is difficult because it requires administering monovalent HBV vaccine and hepatitis B immunoglobulin (HBIg) within 24 hours of birth. Due to the barriers of giving HBIg, the World Health Organization (WHO) states, "…owing to concerns related to supply, safety and cost, the use of HBIg is not feasible in most settings." Clearly, global control of HBV transmission will require improved MTCT prevention. Therefore, the investigators hypothesize that treating HBV early in pregnancy will lead to undetectable HBV DNA levels at delivery and prevention of MTCT of HBV without HBIg; a concept that has already been proven with HIV. Tenofovir disoproxil fumarate (TDF), an approved anti-HBV drug, is promising to prevent MTCT of HBV due to its high potency against hepatitis B and its safety record in pregnant women. A randomized, controlled clinical trial (RCT) will be necessary to determine if TDF given to HBV-infected pregnant women early in pregnancy plus vaccine to the newborn can decrease MTCT of HBV without HBIg. However, before embarking on a RCT, several critical knowledge gaps need to be addressed including the ideal timing for TDF initiation. The purpose of this proposal is to address these knowledge gaps.

The investigators hypothesize that anti-HBV therapy given in the late first or early second trimester achieves undetectable HBV DNA at delivery in >=95% of pregnant women with chronic hepatitis B. The one-arm, open-label, interventional study aims: 1, To estimate the time to complete HBV DNA suppression (<100 IU/ml) in 170 HBV DNA positive women who start TDF in the late first or early second trimester; and to estimate the proportion of women with HBV DNA <100 IU/ml at delivery. 2, To address potential barriers to and the efficacy of implementing TDF in early pregnancy to prevent mother-to-child transmission of hepatitis B. The investigators will measure potential barriers to acceptability and effectiveness of this intervention: adherence, potential hepatitis B flares in mothers (safety), and the proportion of hepatitis B infections in the offspring at 1 year of age (efficacy).

Inclusion Criteria:

• Pregnant women aged 18 and over
• HBsAg positive
• In the 12th-20th week of pregnancy
• Willing to take TDF daily during pregnancy
• Providing written informed consent
• Plans to deliver at Shoklo Malaria Research Unit (SMRU)
• Able and willing to comply with study requirements

Exclusion Criteria:

• Anti-HIV positive
• Negative qualitative HBV DNA if HBeAg negative
• On immunosuppressive therapy
• Elevated creatinine
• History of kidney disease
• Short cervix
• History of pregnancy complications or prior pre-term labor

The investigators are currently developing an individual participant data (IPD) sharing plan.

Data will become available 6 months after publication of the main report.

Permission by corresponding author

No masking, just one interventional group.