1. Baskett, T., Calder, A. and Arulkumaran, S. (2007) Munro Kerr’s Operative Obstetrics, Centenary Edition London: Saunders Elsevier. Figures are reproduced from this text with permission of Elsevier Ltd.
2. Berkley, C. (1922) A Handbook of Midwifery London: Cassell & Company Ltd.
3. Blackburn, S. T. (2013) Maternal, Fetal and Neonatal Physiology: A Clinical Perspective (4th Edition) Maryland Heights: Elsevier Saunders
4. Cronk, M. (no date) My guidelines for the care of a woman expecting twins Mary Cronk Midwifery Services, available online at: http://www.homebirth.org.uk/marycronk/marytwins.htm (Accessed 25 August 2014)
5. Fraser, D. and Cooper, M. (2003) Malpositions of the occiput and malpresentations in Myles Textbook for Midwives, chapter 30, London: Elsevier