Research related to this thesis is published in: Antoniou EE, Derom C, Thiery E, Fowler T, Southwood TR, Zeegers MP. The Influence of Genetic and Environmental Factors on the Etiology of the Human Umbilical cord: The East Flanders Prospective Twin Survey. Biology of Reproduction, 2011 Jul;85(1):137-43 Antoniou EE, Draper H, Reed K, Burls A, Southwood TR, Zeegers MP. An empirical study on the preferred size of the participant information sheet in research. Journal of Medical Ethics, 2011 Apr 8. Epub ahead of print http://eprints.bham.ac.uk/1136/ Antoniou EE, Zeegers MP. The advantage of using twin studies in epidemiological research. British Journal of Obstetrics and Gynaecology, 2011. In press