Objectives To determine the role of placenta in hepatitis B virus (HBV) intrauterine transmission, and to trace the route of transplacental transmission and the timing of HBV infection in uterus.

• 目的探讨乙型肝炎病毒（HBV）宫内传播的危险因素,并追踪HBV经胎盘传播的途径和胎儿宫内感染的时间。