Regional differences in birth prevalence of cleft lip and/or palate in Sweden - a register study of all children born in Sweden between 2000 and 2020.

The birth prevalence of cleft lip and/or palate (CL/P) varies globally, and regional differences have previously been observed within Sweden. Updated data on CL/P birth prevalence is needed and has been requested nationally and internationally. This study investigated regional differences and temporal trends in the birth prevalences of CL/P and specific cleft subtypes across Sweden's six health care regions (HC regions) from 2000 to 2020. Using data from the Swedish Medical Birth Register and the National Register of Congenital Anomalies (coverage 97-99%), the study included 2,230,771 children. Variables included were year and region of birth, and cleft diagnoses: cleft lip and/or palate (CL/P), cleft palate without cleft lip (CP), cleft lip with/without cleft palate (CL ± P), bilateral cleft lip with/without cleft palate (BCL ± P), and unilateral/bilateral cleft lip and palate (UCLP, BCLP). Poisson regression models were used to assess regional differences and trends. The Stockholm HC region had the lowest prevalence for all cleft types except CP. The Northern HC region had a higher CP prevalence, while clefts involving the lip (CL ± P, BCL ± P) were more common in the Southeastern and Southern HC regions. Declining trends were observed in at least two regions for all cleft types except CP. CL/P, CL ± P, and BCL ± P showed decreasing prevalence in three regions. The findings confirm some previously reported regional patterns, including a higher CP birth prevalence in northern Sweden. Potential explanations for the regional differences include genetic variation, differences in attitude towards pregnancy termination, socioeconomic factors, and exposure to other risk factors, but need further examination.