[The role of placenta in hepatitis B virus intrauterine transmission]

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.
Methods: We collected 101 term placentas and newborn infants, 24 aborted first-trimester placentas, and 6 induced aborted fetuses and placentas from 131 HBsAg carrying pregnant women. Serologic HBV markers (HBsAg and HBV DNA) of pregnant women and newborns were detected by ELISA and PCR. The HBsAg, HBxAg, HBcAg and HBV DNA in placentas were determined by ABC immunohistochemical staining and in-situ hybridization.
Results: The HBV infection rates of placentas from first-trimester, second-trimester to term periods were 4.2%(1/24), 1/6, and 44.6%(45/101), respectively. In one induced aborted fetal liver tissue (19-week of pregnancy), the proteins and DNA of HBV were detected, and its placental villous capillary endothelial cells were also infected. The OR of HBV infection of villous capillary endothelial cells in intrauterine transmission was 18.46(95% CI = 2.83-152.78).
Conclusions: HBV infection of placental capillary endothelial cell is a major risk factor of intrauterine transmission. HBV transplacental transmission route may be placental cell to cell transfer. The intrauterine infection may occur as early as on the 19th week of pregnancy, but the main timing is possibly in the third-trimester of pregnancy.