1) Stefos TI, Lolis DE, Sotiriadis AJ, et al : Embryonic heart rate in early pregnancy. J Clin Ultrasound 26 : 33─36, 1998
2) 「超音波胎児計測の標準化と日本人の基準値」の公示について.日本超音波医学会用語・診断基準委員会
3) Pedersen JF : Fetal crown-rump length measurement by ultrasound in normal pregnancy. Br J Obstet Gynaecol 89 : 926─930, 1982
4) Besis R, PaperniK E : Echographic imagery of amniotic membranes in twin pregnancies. In : Twin research 3 : Twin biology and multiple pregnancy. New York : Alan R. Liss, Inc. pp183─187, 1981
5) Finberg H : The twin peak sign : Reliable evidence of dichorionic twinning. J Ultrasound Med 11 : 571─577, 1992
6) Monteagudo A, Timor-Tritsch IE, Sharma S : Early and simple determination of chorionic and amniotic type in multifetal gestations in the first fourteen weeks by high-frequency transvaginal ultrasonography. Am J Obstet Gynecol 170 : 824─829, 1994
7) Carrol GM, Soothill PW, Abdel-Fattah SA, Porter H, Montague I, Kyle PM : Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation. Br J Obstet Gynaecol 109 : 182─186, 2002