Purpose: This study aimed to assess the validity of diagnoses of congenital malformations (CMs) recorded in claims of a university hospital in Japan. Methods: Congenital malformations were identified according to Code Q00–Q89 of the International Classification of Diseases, 10th revision. All the children who had been diagnosed with CMs based on their claims in 2015 and within 1 year from their birth month were selected for this study. The infants' medical records were considered as a gold standard. Positive predictive values (PPVs) for CMs were calculated. Results: This study included 227 infants who had a CM diagnosis in their claims. Based on the algorithms established by the Quebec Pregnancy Cohort study group, the PPV for any CM was 90.7% and that for major CMs (MCMs) was 91.5%. Concerning MCMs of specific organ systems, those of the circulatory system (PPV 85.1%) were the most frequent, followed by cleft lip and cleft palate (PPV 100.0%), and other CMs of the digestive system (PPV 96.4%). Based on the EUROCAT classification, the PPV for any MCM was 88.5%. Specific MCMs reported in ≥20 infants were ventricular septal defect (PPV 96.0%), patent ductus arteriosus (PPV 72.7%) and cleft lip with or without cleft palate (PPV 100.0%). Conclusions: The PPVs for CMs in the Japanese administrative data were high enough to suggest that these data could be utilized for perinatal pharmacoepidemiological evaluations. The results were from a single center, and further validation studies are needed.
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