The risk of vertical HBV transmission is related to HBV DNA level in pregnant women, around 30% in women with HBV DNA above 1, 000 000 I.U/mL despite serovaccination of newborns. Using tenofovir DF during the last trimester of pregnancy allows to reduce the risk, but data from Western countries are needed.

The prevalence of HBs Ag carriage in pregnant women varies in France, according to the native country, with higher rates in those originating from sub-Saharan Africa and Asia (5 to 8% in Parisian area). The level of HBV DNA varies according to HBe status and geographical origin, and is strongly predictive of the risk of HBV mother-to-child transmission (MTCT). The rate of vertical transmission (Yuan J et al. J Viral Hepatitis 2006) was 0% in newborns to mothers with HBV DNA less than 100,000 copies/mL and up to more than 40% in newborns to mothers with HBV DNA above 8 Log10 copies/mL, despite serovaccination at birth, thus justifying the use of tenofovir DF during the last trimester of pregnancy in highly viraemic pregnant women, as mentionned in EASL 2012 Guidelines. Data are needed concerning the results of this strategy in western countries, justifying this prospective study.

Inclusion Criteria:

• pregnant women
• positive for HBs Ag
• HBV DNA above 100,000 I.U/mL

Exclusion Criteria:

• HIV co-infection
• HDV co-infection
• requiring, according to the physician's decision, a treatment for herself and not only to prevent HBV MTC transmission