The cause of intrauterine hepatitis B infection is not yet clear, but there are many studies that have confirmed that the probability of intrauterine hepatitis B infection in the fetus is related to the high infectivity of the pregnant woman. If a pregnant woman is HBeAg positive, has a high HBeAg titer and is positive for HBV-DNA, the probability of intrauterine infection in the fetus is very high. Intrauterine infection of hepatitis B can cause risks such as miscarriage or malformed stillbirth. However, in general, a pregnant woman infected with hepatitis B virus will not affect the fetus. Only small molecules, such as nutrients and oxygen, can pass through the placental barrier, which is a semi-permeable membrane between the mother and the fetus, while large molecules, viruses and bacteria cannot pass through. However, the placental barrier is not yet perfect in early pregnancy, so the hepatitis B virus has the opportunity to enter the fetus during this period. If intrauterine hepatitis B infection occurs, the baby is given hepatitis B immunoglobulin immediately at birth. The hepatitis B vaccine is administered as often and as often as required.