Study of Tenofovir Alafenamide Fumarate Tablets (TAF) in Blocking Mother-to-child Transmission of Hepatitis B Virus

Inclusion Criteria: * maternal age: 20 to 35 years * 20-24 week of gestation * HBsAg-positive more than 6 months and HBeAg-positive * HBV DNA\> 1000,000 IU/ml * both husband and wife voluntarily sign informed consent * with good compliance and comply with follow-up programs Exclusion Criteria: * mother with co-infection of hepatitis C virus,human immunodeficiency virus * evidence of decompensated liver disease * combined with important organ lesions which will affect patient compliance and follow-up plans, pregnant women who are expected to be difficult to complete the study * have a history of spontaneous abortion, or have a birth defect or congenital malformation in the last pregnancy * mother treated with antiviral therapy within 6 months prior to enrollment(except those treated with antiviral therapy in the last pregnancy to prevent mother-to-child transmission) * have a history of kidney injury, creatinine clearance \<50ml/min, urine protein positive (\>300mg/L) * combined with other chronic diseases and need to take immunomodulators, cytotoxic drugs or hormonal drugs during pregnancy * the infants' biologic father is a chronic HBV infected person * symptoms of threatened abortion during early pregnancy * evidence of hepatic cell carcinoma * alanine aminotransferase (ALT) \> 10 x upper limit of normal(ULN ), or total bilirubin (TBIL) \> 3 x ULN or glomerular filtration rate (GFR) \< 90 mL (min\*1.73 m2), or serum Albumin (ALB) \< 25 g/L before enrollment * fetal malformations detected by B-ultrasound * participants in other research