OBJECTIVE: The underlying pathophysiology of preeclampsia is thought to be abnormal trophoblast invasion of the spiral arteries leading to maldevelopment of uteroplacental perfusion. We estimated whether uterine artery Doppler measurements made in the early second trimester would predict the subsequent development of preeclampsia. METHODS: Uterine artery Doppler measurements before 21 weeks of gestation (median 16.6 weeks) were correlated with subsequent development of preeclampsia in a cohort of 2,188 low-risk nulliparous women in a randomized control trial of antioxidant supplementation for prevention of preeclampsia. Preeclampsia developed in 165 (7.5%) women. RESULTS: Development of preeclampsia overall was associated with increased resistance index, pulsatility index, a pulsatility index or resistance index multiple of the median at or above the 75th percentile but not the presence of a notch or a bilateral notch before 21 weeks of gestation. The sensitivity was 43% (95% confidence interval [CI] 35-51) and specificity 67% (95% CI 65-69) for prediction of preeclampsia overall. The presence of a notch or bilateral notch, resistance index, and pulsatility index multiple of the median was significantly associated with early onset (before 34 weeks of gestation) compared with late onset or no preeclampsia (odds ratio [OR] 6.9, 95% CI 2.3-20.9; sensitivity 78%, 95% CI 52-94; specificity 66%, 95% CI 64-68). The presence of a notch or resistance index multiple of the median at or above the 75th percentile increased the odds of developing severe compared with mild or no preeclampsia (OR 2.2, 95% CI 1.4-3.7; sensitivity 53%, 95% CI 40-65; specificity 66%, 95% CI 64-68). CONCLUSION: Our data show poor sensitivity of second-trimester Doppler ultrasound measurements for prediction of preeclampsia overall in a well-characterized, low-risk, nulliparous population. The technique has utility in identifying poor trophoblast invasion of spiral arteries of a magnitude that severely compromises uteroplacental blood flow and gives early-onset disease. © 2012 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.