Since HBV is a blood-borne virus, the unvaccinated pregnant women would be at risk for HBV exposure if their fetuses carried the virus from fathers. On other hand, maternal antibodies can pass through the placenta and enter the fetal circulation freely. If women had been vaccinated for HBV before conception, thus some attractive questions are raised that what would happen to a maternal immune system if her fetus carried HBV from spermatozoa? Would the fetus be passive immunized by hepatitis B immunoglobulin leaked from maternal circulation? However, the literature on transmission of HBV by spermatozoa in vivo is rare, the viral replicating status and fetal immune response in uterus are unknown. Only one study had detected HBV DNA and serological makers on eight aborted fetuses suspected with HBV transmission via spermatozoa, but it is a small sample study and the maternal serological status is uncertain.