6[4]Stampome C, Nicotra M, Muttinelli C, et al. Transvaginal sonography of the yolk sac in normal and abnormal pregnancy. J Clin ultrasound , 1996,24( 1 ): 3
7[5]Crooij MJ, Westhuis J, Schoemaker J, et al, ultragraphic measurement of the yolk sac. Br Jobstet Gynaecol, 1982, 89:931
8[1]周永昌、郭万学主编.超声医学.第4版.北京:科技文献出版社,2002.1025
9陈(亻常)佩,陆兆龄.围生期超声多普勒诊断学.人民卫生出版社,2002.47.
10Crooij MJ,Westhnis J,Schoemaker J,et al.Ultrasonographic measurement of the yolk sac.Br J Obstet Gyraecol,1982,89(11):931.