If there are too many viruses in pregnant women, such as DNA exceeding 108 copy /ml, even if newborns are injected with vaccines and immunoglobulin on time, they may still be infected with the virus. Therefore, European and American doctors have given pregnant women 100 mg lamivudine orally every day since the 33rd week of pregnancy, which is equivalent to adding double insurance, which can significantly reduce perinatal transmission. This method has no adverse reaction and high safety, but it is not recommended to use it in the first three months of pregnancy.