The purpose of this study is to evaluate the efficacy and safety of Tenofovir alafenamide (TAF) for prevention of mother-to-child transmission of hepatitis B virus among pregnant women with high level HBV DNA.

This is a single-arm multicenter, prospective, clinical study, aiming to evaluate the efficacy and safety of Tenofovir alafenamide (TAF) for prevention of mother-to-child transmission of hepatitis B virus among pregnant women with high level HBV DNA. 330 HBV-infected mothers with high level HBV DNA will be enrolled and receive Tenofovir alafenamide (TAF) for prevention of mother-to-child transmission of HBV. Demographic data, antiviral treatment history, pregnancy and labour history, co-morbidity, HBV serologic marker tests, HBV DNA tests, liver function tests, mode of delivery, neonatal characteristics (height, weight, head circumference, Apgar score and any major birth defect), breastfeeding and post vaccination serological test for infants at 7-12 months of age are collected. A mobile health application called "SHIELD" is used in this study to collect data and provide support for communication between mothers and their doctors. All laboratory test reports, questionnaires and other relevant information are uploaded into SHIELD.

Inclusion Criteria:

• Pregnant woman aged 20 to 35 years old
• 24-26 week of gestation
• HBsAg positive more than 6 months and HBeAg positive
• HBV DNA> 200,000 IU/ml
• Informed consent is signed voluntarily by both husband and wife
• Good compliance and able to be followed up as planned

Exclusion Criteria:

• Mothers co-infected with HCV and HIV
• Evidence of decompensated cirrhosis and liver cancer
• Mothers had other organ lesions which would affect patient compliance and follow-up plan
• Mothers had history of spontaneous abortion or their children had birth defect or congenital malformation
• Mothers received antiviral therapy within 6 months
• Mothers had history of kidney injury, CCr <50ml/min and urine protein test positive (>300mg/L)
• Mothers had history of other chronic diseases and had to take immunomodulators, cytotoxic drugs or hormonal drugs during pregnancy
• The infants' biological fathers are infected with HBV
• Symptoms of threatened abortion during early pregnancy
• ALT > 1×upper limit of normal (ULN), or TBIL ≥ 1×ULN or glomerular filtration rate (GFR) < 90 ml/min, or Albumin (ALB) < 25 g/L
• Fetal malformations detected by B-ultrasound during pregnancy
• Participating in other studies

Pregnant woman is eligible for mother-to-child transmission study.