4Vas W, Suresh PL, Tang - Barton P Ultrasonographic Differentiation of cervical abortion from cervical pregnancy. J Clin Ultrasound, 1984,12 (9):553 ~ 557.
5Ushakov FB, Elchalal U, Aceman PJ Cervical Pregnancy: Past and Future. Obstetrical and Gynecological Survey, 1996, 52( 1 ): 45 ~ 56.
6Bader - Armstrong B, Shah Y, Rubens D Use of Ultrasound and Magnetic Resonance Imaging in the Diagnosis of Cervical Pregnancy. J Clin Ultrasound, 1989, 17(4): 283 ~ 286.