Each woman will be informed of the objectives and the total duration of the study as well as the benefits and risks to participate. An information sheet in Khmer will be given to each woman. The study will be composed of two phases of information's and consent. The first one will be done during the HBs Ag screening using rapid test; the screening will be proposed to all pregnant women attending ANC in one of the affiliated centres. The second phase will be done during the inclusion visit and will concern only HBs Ag positive women. The study will concern only HBs Ag positive women with 1) follow up of all HBsAg positive women from inclusion up to 6 months postpartum 2) For HBeAg positive women, initiation of treatment by fumarate de tenofovir disoproxil (Viread®), with a daily administration of one 300mg pill. Women will be treated from 24 weeks of amenorrhea until 6 weeks post-partum. For women with first ANC after 24 weeks of amenorrhea, treatment will begin the day of inclusion. Treatment will be given for 4 weeks and adherence will be estimated. In all cases, vaccination of the newborn will be carried out according to the national protocol in Cambodia i.e. 4 injections at 24 hours, 6, 10 and 14 weeks of age.