1. Baker, E. M.: Pennsylvania Med. J. 48, 29–31 (1944).
2. Bianchi, P.: Tumori 24, 83–100 (1950).
3. Riv. Ostetr. 6, 9–43 (1951).
4. Brewer, J. I., and H. O. Jones: Amer. J. Obstetr. 41, 733–751 (1941).
5. Centaro, A., e G. Serra: Arch. „De Vecchio“ (Firenze) 12, 1031–1054 (1949).