The hepatitis B vaccine currently in use is a genetically engineered vaccine, the main component of which is the surface antigen of the hepatitis B virus, i.e., an outer shell protein of the hepatitis B virus, not an intact virus. This surface antigen does not contain viral genetic material and is not infectious or pathogenic, so it is not harmful to pregnant women or fetuses; at the same time, it retains immunogenicity, i.e., the ability to stimulate the body to produce protective antibodies. The hepatitis B vaccine is administered in three doses at 0, 1 and 6 months, i.e. after the first dose, the second dose is administered one month later and the third dose is administered six months later. Numerous experiments have shown that if pregnant women with hepatitis B virus are effectively immunized before and after delivery, the rate of mother-to-child transmission of hepatitis B virus can be blocked by more than 90%. If a pregnant woman has not been infected with the hepatitis B virus and only wants to prevent hepatitis and protect her fetus from the hepatitis B virus, she can receive the hepatitis B vaccine, still following the 0, 1, 6 procedure. Generally, it takes 3 months for the body to produce antibodies after the vaccination, so that the vaccine virus in the body will disappear completely when the pregnancy occurs and will not cause harm to the fetus; and the hepatitis B vaccine is usually given at least 9 months before the planned pregnancy, because the hepatitis B vaccine requires three injections, and the three injections take 6 months to span, and 3 months are left for the body to produce antibodies. Therefore, it is recommended that the hepatitis B vaccine be given 9 months prior to pregnancy.