1. The spiral twist of the normal umbilical cord in twins and in singletons;Edmonds;Am J Obstet Gynecol,1954
2. The umbilical cord twist: direction, and relevance;Lacro;Am J Obstet Gynecol,1981
3. Observations on the structure of the human umbilical cord;Malpas;Surg Gynecol Obstet,1966
4. The umbilical vessels;Roach,1976
5. A biophysical look at the relationship of structure and function of the umbilical artery;Roach,1973