Eastman, N., & Hellman, L. M. (1961). Williams Obstetrics (12.ed.). Appleton-Century-Croffts.

Eastman, Nicholson, and Louis M. Hellman. Williams Obstetrics. 12.ed. New York: Appleton-Century-Croffts, 1961.

Eastman, Nicholson, and Louis M. Hellman. Williams Obstetrics. 12.ed. Appleton-Century-Croffts, 1961.