Flowchart of data. Flowchart depicts the process by which patient-based and test-based prenatal rubella serology datasets were derived for analysis in this study. The original number of rubella serology tests extracted from the two laboratory information systems used by the Public Health Ontario Laboratory over the study period between 2006 and 2010 is shown (N = 1,048,929). Restricting this dataset to valid prenatal tests conducted on women 15–49 year olds yielded 600,859 tests among 459,963 patients. Further restricting the dataset to tests conducted at least 9 months apart resulted in a total of 551,160 test results available for analysis.