1. Medical Disorders in Obstetric Practice;BARNES, C.G.,1962
2. BELL, A. M. (1952)..Canad. med. Ass. J. 67, 362.
3. EISINGER, R. P. and BERK, H. (1959). Amer. J. Obstet. Gynec. 78, 438.
4. GORDON, G. A. (1927). Amer. J. Obstet. Gynec. 14,633.
5. HAMMAN, L. (1945). J. Amer. med. Ass. 128, 6.