Incidence is the number of new cases of a disorder or condition identified in a specific time period. Prevalence is the number of individuals who are living with the disorder or condition in a given time period.
Epidemiological estimates of orofacial clefts vary substantially on the basis of a variety of factors, including the sample population, the surveillance methodology, and the clinical classification (International Perinatal Database of Typical Oral Clefts [IPDTOC] Working Group, 2011).
Worldwide, oral clefts in any form (i.e., cleft lip, cleft lip and palate, or isolated cleft palate) occur in about one in every 700 live births (World Health Organization [WHO], 2001). International estimates that are limited to cleft lip with or without cleft palate range from 7.94 to 9.92 per 10,000 live births (IPDTOC, 2011; Tanaka, Mahabir, Jupiter, & Menezes, 2012).
Cleft lip with or without cleft palate is the second most common birth defect in the United States, affecting one in every 940 births and resulting in 4,437 cases every year (Parker et al., 2010). Reported prevalence estimates range from 7.75 to 10.63 per 10,000 live births (Parker et al., 2010; Tanaka et al., 2012). Isolated cleft palate is less common, presenting in one in every 1574 births (Parker et al., 2010).
The occurrence rate of orofacial clefts varies by population. Overall, higher rates have been reported in Asians and American Indians (one in 500 births), and lower rates have been reported in African-derived populations (one in 2,500 births; Dixon, Marazita, Beaty, & Murray, 2011). Isolated cleft palate is more frequently found in females than in males, at a ratio of 2:1. In contrast, there is a 2:1 male-to-female ratio for cleft lip with or without cleft palate (Mossey, Little, Munger, Dixon, & Shaw, 2009).