3GRACIA C R,BARNHART K T.Diagnosing ectopic pregnancy:decision analysis 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 M C,VISWESWARAN A,LAING F C.Comparison of tubal ring and corpus luteum echogenicitise:A useful differentiating characteristic[J].J ultrasound Med,2001,20:27-31.
