HBV MTCT is the important reason to keep high prevalence of chronic HBV infection in China; high HBV DNA loads of Pregnant women before delivery is the most important factor resulting in mother-to-child transmission of HBV, therefore, how to drop HBV DNA levels of pregnant women before delivery to the level that can markedly decrease the rate of HBV MTCT on the base of HBIG combined hepatitis b vaccine injection for newborns, which is the most important method to improve HBV MTCT. Although Nucleoside analogue antiviral treatment during late pregnancy can dramatically reduce the rate of HBV MTCT, security problems of NA treatment during pregnancy has not been demonstrated, On account of the above problems, our study is to investigate the effect of starting to use Tenofovir Disoproxil Fumarate(TDF) antiviral treatment from the 32 weeks of gestation to block mother-to-child transmission of hepatitis B virus(HBV MTCT).