1. Prolapse of the umbilical cord
2. N. J. Eastman (1950 ): Williams's Obstetrics , 10th edition , p. 832 . Appleton-Century, New York.
3. T. W. Eden, E. Holland, and A. Brews (1948 ): A Manual of Obstetrics , 9th edition , p. 401 . Churchill, London.
4. G. E. Herman (1929 ): Difficult Labour , 7th edition , p. 94 . Cassell, London.