In this protocol the researchers wish to elaborate prior investigations on factors which may affect prevalence and malarial parasite density in pregnant women in Malawi. Primarily, this investigation will evaluate the efficacy of the current Malawian national policy, sulfadoxine-pyrimethamine (SP) 2-dose intermittent protective treatment (IPT) strategy, and compare it to a monthly SP strategy for use in preventing malaria during pregnancy. Previous investigations in Malawi have demonstrated that: prevention of malaria during pregnancy is most important during the first and second pregnancies, particularly during the rainy season when malaria transmission is highest; and an efficacious antimalarial regimen which clears parasitemia and placental infection will result in a reduction in the incidence of low birth weight, the single greatest risk factor for neonatal and early infant mortality. There appears to be an interaction between HIV infection and placental malaria, with HIV-positive pregnant women having higher prevalences and densities of peripheral and placental parasitemia compared with HIV-negative pregnant women. This finding requires closer examination, in light of the high prevalence and incidence of HIV infection in Malawi and other African countries. Previously in Malawi, a 2-dose IPT regimen of SP administered during the second and third trimester of pregnancy was effective at clearing placental malaria infection at delivery More recent studies in both Malawi and Kenya show that 2 doses may not be adequate in clearing placental parasitemia especially in women who are HIV infected. In the Kenya study, HIV-positive women required 3 doses of SP (that were delivered in a monthly dosing scheme) to achieve similar reductions in placental parasitemia that were seen in HIV-negative women at 2 doses. There remains a need to identify the optimal dosing schedule for an intermittent treatment regimen; the Kenya findings need to be confirmed before decisions are made on national and global levels. This is especially important given the possibility of increasing SP resistance in Malawi. The question of HIV infection and its role in malaria during pregnancy, both in terms of impact on regimen effectiveness and on the incidence of adverse sulfa reactions needs to be examined. This study proposes to determine the efficacy of the current regimen of 2-dose SP intermittent protective treatment (IPT) and to compare it to monthly SP dosing in clearing placental parasitemia at delivery in Machinga district in Malawi where there is a high level of malaria transmission and an HIV seropositivity rate of nearly 20% in reproductive age woman. This study will also explore the effect of HIV seropositivity on the safety and efficacy of intermittent preventive treatment during pregnancy.