INDEX AND SUBSEQUENT PREECLAMPSIA MICHAEL BELFORT, SHLOMIT RISKINMASHIAH, YVETTE LACOURSIERE, MICHAEL VARNER, Society for Maternal-Fetal Medicine, Provo, Utah, Carmel Medical Center, Haifa, Haifa, Israel, University of Utah, Salt lake City, UT, Obstetrics and Gynecology, Salt Lake City, Utah, University of Utah, Obstetrics and Gynecology, Salt Lake City, Utah OBJECTIVE: Pilot study evaluating maternal middle cerebral artery (MCA) Doppler resistance index (RI) as a predictor of impending preeclampsia. STUDY DESIGN: Prospective cohort of 38 normotensive gravidas studied with Doppler MCA RI between 18-22 weeks stratified into two groups: those remaining normotensive and those who developed preeclampsia. Previously published normative MCA Doppler data (Belfort et al. 2001) were used to plot a median RI for normative pregnancy (y = 0.004 + 0.648; R = 0.97). RI data from the study cohort were then plotted and compared with this curve. RI data for both groups were expressed in terms of Multiples of the Median (MOM) from the median curve of normative pregnancy. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and Likelihood Ratio (LR) [with confidence limits] were calculated. Median MOM for preeclamptics was compared with normotensives (Mann-Whitney test). RESULTS: Preeclampsia supervened (n = 7) 13-18 weeks after MCA RI measurement. An RI at 18-22 weeks !0.93 MOM predicted development of preeclampsia with 100% [66-100] sensitivity, 65% [47-79] specificity, 39% [18-64] PPV, 100% [80-100] NPV, and 2.82 [1.75-4.53] LR. Preeclamptics had a lower median RI (0.899 MOM below the normal median; P = .006) than the normotensives (0.969 MOM). CONCLUSION: A low maternal MCA RI between 18-22 weeks gestation may be a selective and reliable predictor of preeclampsia as early as 13-18 weeks before the syndrome appears, and may reflect a generalized maternal hemodynamic response to a circulating placental substance released as a result of poor placental perfusion.