Objective. Few orofacial cleft (OFC) studies have examined the severity of clefts of the lip or palate. This study examined associations between the severity of cleft of the lip with cleft type, laterality, and sex in four regional British Isles cleft registers whilst also looking for regional variations. Design. Retrospective analysis of cleft classification in the data contained in these four cleft registers. Sample. Three thousand and twelve patients from cleft registers based in Scotland, East England, Merseyside, and Belfast were sourced from the period 2002–2010. Submucous clefts and syndromic clefts were included whilst stillbirths, abortuses, and atypical orofacial clefts were excluded. Results. A cleft of the lip in CLP patients is more likely to be complete in males. A cleft of the lip in isolated CL patients is more likely to be complete in females. Variation in the proportion of cleft types was evident between Scotland and East England. Conclusions. Association between severity of cleft of the lip and sex was found in this study with females having a significantly greater proportion of more severe clefts of the lip (CL) and CLP males being more severe . This finding supports a fundamental difference between cleft aetiology between CL and CLP. 1. Introduction Maintaining a register of children born with orofacial clefts is recognised as important with regards to audit, research, and the planning and provision of services . The use of a simple classification, such as the LAHSAL system proposed by Kriens in 1989  to describe clefts is recognised as being of prime importance and allows for the accurate recording of cleft types and comparison between locations . The evidence available at a global and European level indicates very significant regional variation in the birth prevalence of orofacial clefts, both cleft palate (CP) and cleft lip and palate (CLP) . It is well known that the aetiology of orofacial clefts is characterised by heterogeneity and that the aetiology is polygenic multifactorial with both environmental and genetic factors contributing to nonsyndromic type , which comprises approximately 70% of all orofacial clefts. The increase in CP seen in some UK studies and in parts of Scandinavia may be as a result of factors associated with their northern position . The proportion of CP in Sweden was shown to increase with the increase in latitude at which the comparison was carried out . Several studies have shown that females are affected more often than males with regards to isolated CP [6, 8, 9]. Conversely, a
A. W. Smith, A. K. M. Khoo, and I. T. Jackson, “A modification of the Kernahan 'Y' classification in cleft lip and palate deformities,” Plastic and Reconstructive Surgery, vol. 102, no. 6, pp. 1842–1847, 1998.
P. A. Mossey and J. Little, “Epidemiology of oral clefts: an international perspective,” in Cleft Lip and Palate: From Origin to Treatment, D. R. Wyszynski, Ed., pp. 127–158, Oxford University Press, Oxford, UK, 2002.
D. R. Fitzpatrick, P. A. M. Raine, and J. G. Boorman, “Facial clefts in the west of Scotland in the period 1980–1984: epidemiology and genetic diagnoses,” Journal of Medical Genetics, vol. 31, no. 2, pp. 126–129, 1994.
Y. Shapira, E. Lubit, M. M. Kuftinec, and G. Borell, “The distribution of clefts of the primary and secondary palates by sex, type, and location,” Angle Orthodontist, vol. 69, no. 6, pp. 523–528, 1999.
T. A. Gregg, A. G. Leonard, C. Hayden, K. E. Howard, and C. F. Coyle, “Birth prevalence of cleft lip and palate in Northern Ireland (1981 to 2000),” The Cleft Palate-Craniofacial Journal, vol. 45, no. 2, pp. 141–147, 2008.
S. Yuzuriha, A. K. Oh, and J. B. Mulliken, “Asymmetrical bilateral cleft lip: complete or incomplete and contralateral lesser defect (minor-form, microform, or mini-microform),” Plastic and Reconstructive Surgery, vol. 122, no. 5, pp. 1494–1504, 2008.
A. Sivertsen, A. Wilcox, G. E. Johnson, F. ？byholm, H. A. Vindenes, and R. T. Lie, “Prevalence of major anatomic variations in oral clefts,” Plastic and Reconstructive Surgery, vol. 121, no. 2, pp. 587–595, 2008.
E. W. Harville, A. J. Wilcox, R. T. Lie, H. Vindenes, and F. ？byholm, “Cleft lip and palate versus cleft lip only: are they distinct defects?” American Journal of Epidemiology, vol. 162, no. 5, pp. 448–453, 2005.
O. G. Da Silva Filho, M. Santamaria, G. Da Silva Dalben, and G. Semb, “Prevalence of a Simonart's band in patients with complete cleft lip and alveolus and complete cleft lip and palate,” The Cleft Palate-Craniofacial Journal, vol. 43, no. 4, pp. 442–445, 2006.
M. Rittler, J. S. López-Camelo, E. E. Castilla et al., “Preferential associations between oral clefts and other major congenital anomalies,” The Cleft Palate-Craniofacial Journal, vol. 45, no. 5, pp. 525–532, 2008.