The association between antidepressant use and assisted reproductive technology (ART) treatment in Danish women: A national registry-based cohort study

The Danish Civil Registration System (CRS) was established in 1968, and all persons alive and living in Denmark were registered for administrative use. CRS includes individual information on the unique personal identification number, name, gender, date of birth, place of birth, citizenship, identity of parents and continuously updated information on vital status, place of residence and spouses. Since 1968, CRS has recorded current and historical information on all persons living in Denmark. Among persons born in Denmark in 1960 or later it contains complete information on maternal identity. For women born in Denmark in April 1935 or later it contains complete information on all their children. CRS contains complete information on immigrations and emigrations from 1969 onwards, permanent residence in a Danish municipality from 1971 onwards, and full address in Denmark from 1977 onwards. CRS in connection with other registers and biobanks will continue to provide the basis for significant knowledge relevant to the aetiological understanding and possible prevention of human diseases.

The Danish National Patient Register (NPR) was established in 1977, and it is considered to be the finest of its kind internationally. At the onset the register included information on inpatient in somatic wards. The content of the register has gradually been expanded, and since 2007 the register has included information on all patients in Danish hospitals. Although the NPR is overall a sound data source, both the content and the definitions of single variables have changed over time. Changes in the organisation and provision of health services may affect both the type and the completeness of registrations. The NPR is a unique data source. Researchers using the data should carefully consider potential fallacies in the data before drawing conclusions.

Individual-level data on all prescription drugs sold in Danish community pharmacies has since 1994 been recorded in the Register of Medicinal Products Statistics of the Danish Medicines Agency. The register subset, termed the Danish National Prescription Registry (DNPR), contains information on dispensed prescriptions, including variables at the level of the drug user, the prescriber, and the pharmacy. Reimbursement-driven record keeping, with automated bar-code-based data entry provides data of high quality, including detailed information on the dispensed drug. The possibility of linkage with many other nationwide individual-level data sources renders the DNPR a very powerful pharmacoepidemiological tool.