3Gracia CR, Barnhart KT. Diagnosing ectopic pregnancy: decision analy-sis comparing six strategies [J]. Obstet Gynecol, 2001, 97:464-470.
4Ludwig M, Kaisi M, Bauer O, et al. Heterotopic pregnancy in a spontaneous cycle: do not forget about it [J]. Eur J Obstet Gynecol Reprod Biol, 1999, 87:91-93.
5Frates MC, Visweswaran A, Laing FC. Comparison of tubal ring and corpus luteum echogenicitise:A useful differentiating characteristic [J]. J UItrasound Med, 2001, 20:27&31.
6Wherry KL, Dubinsky YJ, Waitches GM, et al. Low-resistance endometrial arterial flow in the exclusion of ectopic pregnancy revisited [J]. J UI-trasound Med,2001,20:335-342.
7Orden MR,Gudmundsson S,Helin HL,et al. Intravascular contrast agent in the ultrasonography of ectopic pregnancy [J]. Uirasound Obstet Gynecol,1999,14:348-352.
8Kucera E,Helbich TH,Klem I,et al. Systemic methotrexate treat - ment of interstitial pregnancy - magneric resonance imaging (MRI) as avaluable tool for monitoring treatment [J]. Wien Klin Wochenschr,2000,112:772-775.
10Dart R,Dart L,Mitchell P,et al. The utility of a dilatation and evacuation procedure in patients with symptoms suggestive of ectopic pregnancy and indeterminate transvaginal ultrasonography [J]. Acad Emerg Med,1999,6:1024-1029.