<qa>  What is the main cause of malaria?It has been demonstrated that malaria is responsible for anaemia during pregnancy and reduces birth weight among newborns. In Bolivia, malaria is mostly caused by P. vivax. Maternal and foetal consequences of P. vivax infections have been poorly investigated until now, over all in South America. In fact, recommendations for the protection of pregnant women from malaria in Bolivia have not been clearly established. Prophylaxis by chloroquine is still recommended in other continents than Africa, mainly because chloroquine resistances are still uncommon in P. vivax species. The alternative way to protect women during pregnancy is to treat malaria attacks during antenatal visits. For this purpose, we will realize a study in order to assess the most appropriate way to protect women and foetus from malaria infection, i.e. weekly prophylaxis or mild malaria attack treatment, both by chloroquine. By realizing a randomized and multicentric clinical trial on 800 women in each group, we will compare the impact on maternal malaria attack incidence rates, on proportions of mothers with anaemia, on low-birth weight and on positive parasitaemias during pregnancy and at delivery, of weekly prophylaxis and mild malaria attack diagnosis and treatment. The study will be undertaken during 18 months in the region of Santa Cruz and will give important information to the Bolivian Ministry of Health for establishing national recommendations. 