Cases of pregnancy-induced hypertension were identified from ICD-9 codes. Four separate case groups were created based o

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Cases of pregnancy-induced hypertension were identified fromICD-9 codes. Four separate case groups were created based on thesecodes: eclampsia (ICD-9 code 642.6, n = 154), severe preeclampsia(ICD-9 code 642.5, n = 1,180), mild preeclampsia (ICD-9 code 642.4,n = 5,468), and gesta- tional hypertension (ICD-9 code 642.3, n =8,943). All cases identified during the study period were included.Controls (n = 47,237) were defined as women who did not have any ofthe above diagnoses. Controls were randomly sampled from each yearof the study and were frequency matched to the cases by year ofbirth. There were 215,897 total possible controls from which thissample was drawn.
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