Cleft lip and palate versus cleft lip only: are they distinct defects?

Cleft lip defects are usually regarded as a single entity, with the assumption that an accompanying cleft palate represents the more severe form. The authors linked data from the Medical Birth Registry of Norway with medical records from two centralized centers to provide a population-based data set. They assessed the distribution of cleft lip only and cleft lip with cleft palate by covariate. Among 1.8 million Norwegian livebirths between 1967 and 1998, there were 1,572 cases of cleft lip with cleft palate and 1,122 cases with cleft lip only. Seventeen percent of those with cleft lip and palate had another defect compared with 9% of those with cleft lip only. For boys, the risk was greater for cleft lip and palate than for cleft lip only (odds ratio=2.4 vs. 1.8, p<0.001 for difference). The risk of cleft lip only, but not of cleft lip and palate, was increased for twins (odds ratio=1.6 vs. 1.1, p=0.11) and infants whose parents were first cousins (odds ratio=2.7 vs. 0.7, p=0.07). Although cleft lip with cleft palate may simply represent a more severe form of the defect, epidemiologic assessments of cleft lip should, when possible, include separate analyses of these two groups.