Malaria is caused by a parasite and is a health problem for mothers and fetuses (unborn infants). The Cameroonian Ministry of Health recommends that all pregnant women should take the drug sulfadoxine-pyrimethamine (also known as SP) every two months during pregnancy to avoid malaria. The purpose of this study is to find out how effective SP is in preventing pregnant Cameroonian women from getting malaria. Additional goals of this study are to see whether: SP prevents malaria parasites from causing changes in the placenta; SP prevents or helps women make a substance that keeps parasites from accumulating in the placenta; and whether SP affects the amount of protection a mother transfers to her baby. Participants will include 1,160 pregnant women, ages 15-50 years, and 216 babies born residing in Ngalii II and Ntouessong. Study procedures will include monthly blood samples from pregnant women and babies. Volunteers may participate in this study for up to 19 months.