BACKGROUND: Data from hospital-based registers and medical records offer valuable sources of information for clinical and epidemiological research purposes. However, conducting high-quality epidemiological research requires valid and complete data sources.

OBJECTIVE: To assess completeness and validity of a hospital-based clinical register - the Obstetric Database - using a national register and medical records as references.

METHODS: We assessed completeness of a hospital-based clinical register - the Obstetric Database - by linking data from all women registered in the Obstetric Database as having given birth in 2013 to the National Patient Register with coverage of all births in 2013. Validity of eleven selected indicators from the Obstetric Database was assessed using medical records as a golden standard. Using a random sample of 250 medical records, we calculated proportion of agreement, sensitivity, specificity, and positive and negative predictive values for each indicator. Two assessors independently reviewed medical records and inter-rater reliability was calculated as proportion of agreement and Cohen's κ coefficient.

RESULTS: We found 100% completeness of the Obstetric Database when compared to the Danish National Patient Register. Except for one delivery all 6,717 deliveries were present in both registers. Proportion of agreement between the Obstetric Database and medical records ranged from 91.1% to 99.6% for the eleven indicators. The validity measures ranged from 0.70 to 1.00 indicating high validity of the Obstetric Database. κ coefficients from the inter-rater reliability ranged from 0.71 to 1.00.

CONCLUSION: Completeness and validity of the Obstetric Database were found acceptable when using the National Patient Register and medical records as golden standards. The Obstetric Database therefore offers a valuable source for examining clinical, administrative, and research questions.