Uterine artery Doppler at 11 + 0 to 13 + 6 weeks and 21 + 0 to 24 + 6 weeks in the prediction of pre-eclampsia - Plasencia, W; Maiz, N; Poon, L; Yu, C; Nicolaides, K H (Ultrasound Obstet Gynecol, 2008)