1Stefos T, Plachouras N, Sotiriadis A, et al. Routine obstetrical ultrasound at 18-22 weeks: our experience on 7,236 fetuses. J Matem Fetal Med,1999,8(2) :64-69.
2Campbell MF, Harrison JH. Anomalies of the ureter//Campbell MF, Harrison JH. Urology, vol. 2 , 3rd ed. Philadelphia, PA : W. B. Saunders, 1970 : 1488,1800.