The University of California Study of Outcomes in Mothers and Infants (a Population-Based Research Resource): Retrospective Cohort Study.

backgroundPopulation-based databases are valuable for perinatal research. The California Department of Health Care Access and Information (HCAI) created a linked birth file covering the years 1991 through 2012. This file includes birth and fetal death certificate records linked to the hospital discharge records of the birthing person and infant. In 2019, the University of California Study of Outcomes in Mothers and Infants received approval to create similar linked birth files for births from 2011 onward, with 2 years of overlapping birth files to allow for linkage comparison.

objectiveThis paper aims to describe the University of California Study of Outcomes in Mothers and Infants linkage methodology, examine the linkage quality, and discuss the benefits and limitations of the approach.

methodsLive birth and fetal death certificates were linked to hospital discharge records for California infants between 2005 and 2020. The linkage algorithm includes variables such as birth hospital and date of birth, and linked record selection is made based on a "link score." The complete file includes California Vital Statistics and HCAI hospital discharge records for the birthing person (1 y before delivery and 1 y after delivery) and infant (1 y after delivery). Linkage quality was assessed through a comparison of linked files and California Vital Statistics only. Comparisons were made to previous linked birth files created by the HCAI for 2011 and 2012.

resultsOf the 8,040,000 live births, 7,427,738 (92.38%) California Vital Statistics live birth records were linked to HCAI records for birthing people, 7,680,597 (95.53%) birth records were linked to HCAI records for the infant, and 7,285,346 (90.61%) California Vital Statistics birth records were linked to HCAI records for both the birthing person and the infant. The linkage rates were 92.44% (976,526/1,056,358) for Asian and 86.27% (28,601/33,151) for Hawaiian or Pacific Islander birthing people. Of the 44,212 fetal deaths, 33,355 (75.44%) had HCAI records linked to the birthing person. When assessing variables in both California Vital Statistics and hospital records, the percentage was greatest when using both sources: the rates of gestational diabetes were 4.52% (329,128/7,285,345) in the California Vital Statistics records, 8.2% (597,534/7,285,345) in the HCAI records, and 9.34% (680,757/7,285,345) when using both data sources.

conclusionsWe demonstrate that the linkage strategy used for this data platform is similar in linkage rate and linkage quality to the previous linked birth files created by the HCAI. The linkage provides higher rates of crucial variables, such as diabetes, compared to birth certificate records alone, although selection bias from the linkage must be considered. This platform has been used independently to examine health outcomes, has been linked to environmental datasets and residential data, and has been used to obtain and examine maternal serum and newborn blood spots.