In this double-blinded randomized clinical trial study we would like to compare the effect of high dose (5 mg daily) and low dose (1 mg daily) of folic acid supplementation on prevalence, onset and severity of preeclampsia. nine-hundred pregnant women who are in first trimester with sigelton or twin pregnancy and referred to Shahidbeheshti and Alzahra university hospitals of Isfahan-Iran for two years (10/10/91 and 9/10/93) that not conterasndication of folic acid with satisfaction will include in to the study and if fetal death during the study, major abnormality of the fetus, women who were planning to move outside of the catchment area of the study within the pregnancy duration left study. They are divided randomized computer into two groups of 5mg (treated with daily 5 mg of folic acid) and 1mg (treated with daily 1 mg of folic acid).The first assessment of women was done about complete medical and obstetrical history, physical exam, demographic data (age, weigh, height, BMI and gravidity), calculating gestational age, vital sign (specially systolic and diastolic blood pressure and laboratory data including urine analysis, platelet count, liver function tests (including AST and ALT) and serum's creatinine and making prenatal card. and platelet count will evaluated in a 9-months clinical follow up . The study participants were pregnant women who have received prenatal cares at the study clinics since first visit to delivery for sign of preeclampsia and followed up at least 42 days after child birth in this clinics.