China is a major hepatitis B (HBV) country, with about 130 million people currently infected with the hepatitis B virus, of which mother-to-child transmission is a very important route. However, studies have shown that the public and even medical personnel in China do not have enough knowledge about preventing mother-to-child transmission of hepatitis B. For example, up to 87% of medical personnel wrongly believe that newborns of HBV-infected mothers cannot be breastfed. How to carry out effective immunization against hepatitis B is a key measure to interrupt mother-to-child transmission. 1, HBV mother-to-child transmission route and risk factors: HBV mother-to-child transmission route is the same as ordinary infection, that is, the virus through the broken skin mucosa into the blood circulation. Fetal and neonatal skin mucous membranes are thin and tender and prone to produce tiny wounds. There is no evidence of HBV transmission through the fetal or neonatal gastrointestinal tract, nor is there evidence of mother-to-child transmission through germ cells (U cells and sperm/semen) and placental trophoblast cells. Mother-to-child transmission of HBV can be divided into: (1) Prenatal transmission: intrauterine infection, also known as vertical transmission, for which immunoprophylaxis is ineffective. Immunoprophylaxis of newborns of HBsAg-positive and HBeAg-negative mothers is almost free of infection, proving that true prenatal transmission is rare, with an overall estimate of less than 3%. (2) Intrapartum transmission: Mother-to-child transmission is most likely to occur at this time, and immunoprophylaxis is effective. (3) Postpartum transmission: less likely and immunoprophylaxis is effective. The risk factor for the occurrence of mother-to-child transmission is the viral load of the pregnant woman, i.e., the level of HBV DNA. Some people consider HBV DNAR106 copies/m1 or 2 X 105 U/ml as high viral level, but some studies consider HBV DNAR108 copies/ml or 2 X 107 U/ml as high risk factor. HBeAg has good correlation with HBV DNA level, and positive HBeAg can indicate high viral load. The results of HBeAg detection by domestic reagents are stable and reliable, and are suitable for hospitals at all levels. Therefore, HBeAg positivity as a high-risk factor for mother-to-child transmission is more suitable for our national situation. In addition, the mode of delivery is not related to mother-to-child transmission of HBV. HBV can be present in breast milk, and the virus may be released from cracked nipples, etc. However, HBV is not transmitted through the digestive tract, and newborns are already immune after taking immunoprophylaxis. Breastfeeding does not increase the risk of mother-to-child transmission, and breastfeeding should be encouraged, and breast milk does not need to be tested for HBV-DNA. Abnormal liver function during pregnancy is not a risk factor for mother-to-child transmission, but one needs to be alert for the tendency to develop heavy hepatitis, and if necessary If necessary, a consultation with an infection or hepatologist is required. Exposure is a prerequisite for infection, but exposure does not necessarily mean infection. If a pregnant woman is positive for HBsAg, her newborn baby must be exposed to HBV during delivery (including cesarean section), and there can be a small amount of virus in human blood, but the infection has not yet formed at this time. In addition, 10%-20% of pregnant women with HBsAg can enter the fetus through the placenta, and 70%-80% of pregnant women with positive hepatitis B e antigen (HBeAg) have HBeAg that can pass through the placenta, but these antigens are not complete viruses, and it takes up to 6 months to clear. Therefore, testing cord blood or peripheral blood from infants younger than 6 months of age with a positive HBV marker for any one of them is not diagnostic of mother-to-child transmission; it must be tested at 7 to 2 months of age, at which point mother-to-child transmission can be established if HBsAg is positive. Therefore, there is no need for routine clinical testing of cord blood or HBV markers in infants younger than 6 months of age. If the mother is negative for HBsAg, her newborn baby will be vaccinated against hepatitis B according to the “0, 1, 6 months” program, and chronic infection will rarely occur again. If the mother is HBsAg-positive, her newborn will be given hepatitis B immunoglobulin (HBIG) within 12 hours of birth and vaccinated according to the “0, 1, 6 months” protocol. The use of HBIG in late pregnancy is not effective in preventing mother-to-child transmission, and the advantages and disadvantages of antiviral treatment during pregnancy to reduce mother-to-child transmission need to be further studied. The active ingredient of the hepatitis B vaccine is HBsAg, which causes the body to actively produce hepatitis B surface antibodies (anti-HBs) for active immunity. After the first dose of vaccine, most anti-HBs are still negative or below the lower limit of detection, and the anti-HBs will only turn positive about 1 week after the second dose, thus creating protection. Therefore, the second dose of vaccine must be administered on time in order to provide the expected protection, and delaying the first and/or second dose will reduce the effectiveness of the vaccine. The purpose of the 3rd dose is to increase the anti-HBs significantly and extend the protection period. The anti-HBs positive conversion rate of newborns after full vaccination is about 95% and the protection period is more than 20 years. Hepatitis B immunoglobulin (HBIG) is a total IgG extracted from the blood of healthy people with high titers of anti-HBs positivity, and the active ingredient is anti-HBs. It should be noted that HBIG must be injected at a different site from the hepatitis B vaccine, and the earlier the injection, the better the effect, generally the best effect within 1 h, better within 24 h, and still have some effect within 3 d. More than 3 d is basically ineffective for infection at delivery, and only effective for postpartum infection. The half-life of anti-HB s in HBIG in vivo is 21-23 d. The level of protection of anti-HBs in vivo (R10 mU/m1) can be maintained for at least 2 half-lives (42 d) after 100 U injection in newborns; for 200 U injection, it can be maintained for at least 3 half-lives (63 d). Newborns can produce anti-HBs about 1 week after the 2nd dose of hepatitis B vaccine (37 d after birth), therefore, the 2nd dose of HBIG is generally not necessary. if newborns are not vaccinated in time for various reasons, or if premature infants have poor immune response to the vaccine, the 2nd dose of HBIG needs to be given at 3-4 weeks of age.