Calcium Supplementation to Prevent Preeclampsia in Sichuan Province of China

Inclusion Criteria: * Nulliparity;age ≥35 years;Previous pre-eclampsia;Family history of pre-eclampsia;Multiple pregnancy;Time between pregnancies ≥10years;Body mass index ≥25;diastolic pressure ≥ 80 mm Hg before 20 weeks' gestation;Proteinuria ≥+ on more than one occasion or ≥ 300 mg/24 h before 20 weeks' gestation;Underlying medical conditions(Pre-existing hypertension;Pre-existing renal disease;Pre-existing diabetes;Presence of antiphospholipid antibodies;Chronic autoimmune disease);male sex partner's predecessor wife has Previous pre-eclampsia Exclusion Criteria: * first prenatal visit after 16 weeks' gestation;severe anemia;other Underlying medical conditions which need treatment first (such as uncontrolled hyperthyreosis )