A comparative study of folate and vitamin B 12 serum levels in preeclamptic versus normotensive pregnant women in correlation with uterine and umbilical artery Doppler findings and pregnancy outcome Normotansif ve preeklamptik gebelerde serum folat ve vitamin B12 düzeylerinin uterin ve Umbilikal arter Doppler sonuçlari ve gebelik sonuçlariyla karşilaştirilmasi