1. The Influence of Social and Economic Factors on Stillbirths and Neonatal Deaths
2. J. B. DeLee, and J. P. Greenhill (1947 ): Principles and practice of obstetrics ., 9th edition. Philadelphia, p. 767 .
3. J. B. DeLee, and J. P. Greenhill , (1947 ): Principles and practice of obsterics ., 9th ed. Philadelphia, p. 751 :