Pregnant women admitted to the study will continue with their normal attendance at IMIP or HDM. There will be no interference by the researchers in obstetric management of patients involved in the study. All pregnant women will be followed until the postpartum and the newborn until hospital discharge.Hematologic and urine tests will be performed every month (four times) to evaluate Mg++ concentration from each pregnant woman. After inclusion in the study, pregnant women will be monitored monthly until delivery. Pregnant women who do not attend the clinic visit schedule, will be contacted by phone and/or visited. Losses after randomization will be registered with the respective reason.