Spontaneous Adverse Drug Reaction Reporting of Congenital Malformations: A Danish National Register Study

<b>Background/Objectives</b>: Maternal use of medication during pregnancy may have teratogenic effects, as seen with drugs like thalidomide, valproate, and phenytoin. Despite rigorous testing, both new and established drugs still pose a risk of teratogenesis, particularly if the teratogenic effects are probabilistic and not deterministic. Public health organizations maintain registers to centralize and evaluate adverse drug reactions (ADR). However, underreporting in these registries can obscure the signals of drug-related congenital malformations. This study aims to evaluate potential ADR-associated congenital malformations in Denmark over the past decade; <b>Methods</b>: An observational cross-sectional study was conducted using data from the national Danish Medicines Agency's pharmacovigilance database, which includes all spontaneous ADR reports submitted to the Danish Medicines Agency from 1 July 2013 to 30 June 2023. Maternal antenatal drug use was identified, and reported ADRs were assessed for congenital malformations; <b>Results</b>: We identified reports of potential ADR-related congenital malformations in 75 children, with 92 diagnoses as classified by ICD-10. Eighty-five different drugs from 58 ATC codes were implicated. Only three diagnoses were reported in five or more children. The reports were generally sporadic, with no new signals detected; <b>Conclusions</b>: Public awareness is crucial when novel threats arise from medications, infections, or technologies, as these may pose risks to unborn children. Ongoing monitoring of potential ADR-related congenital malformations remains a critical component of public health. Given the potential underreporting, we encourage a low threshold for reporting ADRs based on suspicion alone, with final causality assessments made by health authorities.