Mother-to-child transmission is mainly through infection in the birth canal or intrauterine infection with the same disease as the mother. It is also called vertical transmission because it is transmitted from mother to offspring: HIV, hepatitis B and other diseases are transmitted in this way. Therefore, it is important to be very careful when a person with hepatitis becomes pregnant so that the child does not get the disease during delivery. Mother-to-child transmission of hepatitis B is the transmission of the hepatitis B virus from pregnant women to their offspring and occurs in three main periods: prenatal, perinatal and postnatal. Prenatal transmission, or intrauterine transmission, is when the hepatitis B virus infects the fetus through the placenta. This route of transmission is still debated, and some believe that virus particles cannot cross the placental chorionic membrane barrier. However, after much medical research and observation, it has been found that hepatitis B virus can pass through the broken placenta and cause intrauterine infection. The most serious route of transmission is intrapartum transmission, i.e. the fetus passes through the mother’s birth canal during delivery and swallows maternal blood, amniotic fluid, vaginal secretions, and feces containing hepatitis B surface antigen, causing infection. Postnatal transmission refers to close mother-infant contact after delivery, exposing the newborn to the hepatitis B virus, which is mainly associated with swallowing the mother’s saliva and breastfeeding.