Isolated oral clefts and school grades: population-based cohort study from Norway

OBJECTIVE: To compare school grades of adolescents in Norway born with isolated cleft with those of their unaffected peers. DESIGN: Population-based cohort study. SETTING: Norway. PATIENTS: A total of 347 419 individuals born in Norway between 1986 and 1992, including 523 isolated cleft cases which were identified using data from Norway’s two treatment centres. Individuals were followed from birth through compulsory school. MAIN OUTCOME MEASURES: Grade point average (GPA) from middle school graduation (around the age of 16). Specific subject grades were also investigated. RESULTS: Using a grade scale from 1–6, the observed mean GPA for the reference group was 3.99. Both cleft lip only (CLO) and cleft lip with cleft palate (CLP) had a mean GPA similar to the reference group (adjusted GPA differences from the reference with 95% CIs of 0.06 (−0.04 to 0.16) and −0.08 (−0.19 to 0.03), respectively). Cleft palate only (CPO) had a marginally lower GPA (adjusted GPA difference: −0.18 (−0.28 to −0.08)). These comparisons were consistent across specific subjects. Overall, the evidence suggests a larger difference in GPA between cases and controls in males compared with females. Females with CLO even had a higher estimated GPA than females in the reference group (adjusted GPA difference: 0.19 (0.013 to 0.36)). Grades were similar regardless of laterality of cleft lip (CLO or CLP). CONCLUSION: In Norway, individuals born with isolated CLO or CLP did not have lower average school grades when graduating from middle school. Individuals born with isolated CPO had marginally lower grades.