Mother-to-child transmission: The rate of HBV carriage among pregnant women in China is about 11.0% ~ 12.5%, and among pregnant women with positive serum HBsAg, 45.4% of them are also positive for serum HBsAg. The chance of mother-to-child transmission among mothers with HBsAg is 40% ~ 70%, and if the mother is double positive for HBsAg and HBeAg, the rate of mother-to-child transmission rises to 90% ~ 100%. Mother-to-child transmission occurs from the last 3 months of pregnancy to the first 2 months after delivery, and includes 3 routes: (1) in utero infection or prenatal transmission, accounting for about 5%-15% of mother-to-child transmission, maternal HBV transmission through the placenta or germ cells; (2) transmission during labor, accounting for more than 80% of mother-to-child transmission, for maternal HBV during labor due to contractions, which can cause maternal blood to seep into the fetus, or Newborns in the birth canal through the oral intake of maternal blood, amniotic fluid and vaginal secretions, as well as in the delivery of newborns through the skin and mucous membranes and be infected; (3) postnatal transmission, accounting for less than 10% of mother-to-child transmission, HBV positive mothers through breastfeeding, mouth-to-mouth feeding, menstrual blood and saliva will be infected with HBV to infants. Mother-to-child transmission is the main cause of the aggregated family distribution of hepatitis B. Family aggregation is a phenomenon that presents multiple cases of hepatitis B or HBV infection in one household in areas with high hepatitis B prevalence.