['MTHFR C677T polymorphism is a genetic factor increasing both risk factors for atherosclerotic vascular diseases and obstetric complications like preeclampsia (PE) and fetal growth restriction (FGR). Increased uterine artery impedance, measured by uterine artery Doppler in the second trimester of pregnancy is also associated with PE and FGR. In this study we aimed to analyze whether MTHFR influences first and second trimester uterine artery impedance.', 'In a prospective, controlled, open, single center study of 1955 consecutive singleton pregnant women, smears from buccal gingival cells were analyzed for MTHFR by hybridisation on micro arrays. Uterine artery PI values and unilateral or bilateral diastolic notch were measured at 12 and 22 weeks of gestation. Statistical significance was calculated by the x(2)-test.', 'MTHFR C677T polymorphism showed a normal distribution in our population. Mean uterine artery Doppler values and bilateral or unilateral notch occurrences from 1697 statistical evaluated women did not show significant differences in any MTHFR genotype (C/C, C/T, T/T) both at 12 or 22 weeks of gestation.'] Does carriage of the methylenetetrahydrofolate reductase ( MTHFR ) C677T polymorphism influence the first and second trimester uterine artery Doppler flow?