Comprehensive analysis of uterine artery flow velocity waveforms for the prediction of pre-eclampsia

Objectives To evaluate the performance of velocimetric indices of uterine artery flow velocity waveforms (FVW's) at 20 weeks' gestation, alone or in combination with qualitative analysis, and establish the optimal screening method for the prediction of pre-eclampsia. Methods A total of 614 primiparous women had color flow/pulsed Doppler (CFPD) imaging of both uterine arteries at 20 weeks gestation. Receiver operator characteristic (ROC) curves were created for the systolic/end-diastolic (A/B) ratio, resistance index (RI) and systolic/ early diastolic (A/C) ratio for placental and non-placental uterine arteries, individually or in combination with the presence of unilateral or bilateral notches. Based on data from ROC curves, the sensitivity of each method was compared with the false-positive rate set at 17 and 11%. Results The highest sensitivity (88%) and specificity of (83%) was obtained using bilateral notches/mean RI greater than or equal to 0.55 (50th centile) and unilateral notches/mean RI greater than or equal to 0.65 (80th centile). When the false-positive rate was set at 17%, the inclusion of bilateral notches significantly improved the sensitivity of RI (P <0.001), placental RI (P <0.02), placental A/C ratio (P < 0.05), mean A/C ratio (P < 0.01) and mean A/B ratio (P < 0.05). Bilateral notches/mean RI or A/B cut-offs were also superior to the persistence ofa notch in either artery combined with RI (P < 0.01) or A/B ratio (P < 0.05). When the false-positive rate was set at 11%, the inclusion of bilateral notches did not improve the sensitivity of the A/C (P =1.00) or A/B ratio (P > 0.10). Placental velocimetric indices performed better than mean indices but the differences in sensitivity at the set false-positive rates were not statistically significant. Conclusion At 20 weeks' gestation, bilateral notches with mean RI cut-offs is the best screening method if further screening later in pregnancy is proposed. The AIC ratio is complementary to bilateral notches when the false-positive rate is set at 17% and an effective quantitative substitute when the false-positive rate is set at 11%.