To evaluate the efficacy of 2 grams per day of oral calcium supplementation in reducing the combined incidence of hypertensive disorders of pregnancy: pre-eclampsia, eclampsia, and the HELLP Syndrome (hypertension, thrombocytopenia, hemolysis, and abnormal liver function). The National Institute of Child Health and Human Development (NICHD) initiated the trial in 1991, with joint funding provided by the National Heart, Lung, and Blood Institute in fiscal years 1992, 1993, and 1995.