The appearance of end-diastolic flow velocities (EDF) in the umbilical artery (UA), usually between 10 and 14 weeks of gestation, has been associated with the opening of the spiral arteries and consequently of the intervillous space. The aim of our study was to compare first trimester UA pulsatility index (PI) and EDF between women who developed preeclampsia (cases) and controls. Our database was searched for cases who had UA Doppler between 10-14 weeks. UA PI and EDF were compared between cases and two gestational age (GA) matched controls. 15 cases with severe preeclampsia (PE) were matched to 30 controls. GA with negative EDF was lower than with positive EDF (12.1±0.79 vs. 12.8±0.34; p=0.001). UA PI in cases was higher than in controls, although not significant (cases: 2.18±0.6 vs. 1.92±0.48; p=0.12). However, comparing groups with negative EDF, the difference became significant (PI cases: 2.45±0.57 vs. PI controls: 1.94±0.56; p=0.038), while no difference was found comparing groups with positive EDF. First trimester UA PI is significantly higher in women which will develop PE than in controls. Interestingly, the timing of screening for PE by UA Doppler seems to play an important issue.