Aus anti (HBsAg) positive mothers can transmit HBV to their offspring. Its predominant occurrence is during and after delivery, whereas vertical transmission (intrauterine infection before delivery) is <3%, mostly in pregnant women with a positive hepatitis B E antigen (HBeAg). The screening HBV serologic markers (commonly known as hepatitis B two-and-a-half pairs) include HBsAg, anti-HBs (hepatitis B surface antibody), HBeAg, anti-HBe (hepatitis B e antibody), and anti-HBc (hepatitis B core antibody). The clinical diagnostic significance of their screening is that if HBsAg is positive, it indicates that HBV is replicating and is infectious; if HBeAg is positive, it indicates high viral load, active HBV replication and high infectivity. Anti-HBs is a neutralizing antibody, and serum anti-HBs level ≥10mIU/mL is protective for the body (Table 1). Fluorescence quantitative RT-PCR can detect the HBV-DNA level of HBV and reflect the high or low HBV load. However, the HBV-DNA of “small triplets” (about 30% of pregnant women who are HBsAg positive and HBeAg negative) and even a few “large triplets” (those who are HBeAg positive) is below the lower limit of the normal range of detection, which is called “HBV-DNA is negative”, there is still HBV in the blood and it is infectious. When a pregnant woman is positive for HBsAg, regardless of her HBV-DNA level, or even “negative”, immunoprophylaxis should be taken for the newborn she delivers in order to avoid infection in the newborn.