Pregnancy is possible 1 month after the 3rd dose of the preventive hepatitis B vaccine and the hepatitis B vaccination does not have an adverse effect on pregnancy. Hepatitis B vaccine is a purified hepatitis B surface antigen, a dead vaccine, and a special drug used to prevent hepatitis B. The vaccination stimulates the immune system and produces protective antibodies. Such antibodies exist in the human blood, and once the hepatitis B virus appears the antibodies will work immediately to remove it and prevent infection, and the hepatitis B vaccination will not have an adverse effect on pregnancy. Hepatitis B vaccination is administered as a preventive vaccination at 0, 1 and 6 months of age. Pregnancy is not recommended during the vaccination period because a few people will experience adverse reactions after hepatitis B vaccination, such as fever, nausea, loss of appetite or redness and swelling at the vaccination site to varying degrees. In case of serious abnormalities, it is important to go to the hospital promptly.