Validity of hypertensive disorders of pregnancy diagnoses in the Swedish pregnancy register using a contemporary cohort

INTRODUCTION: The validity of hypertensive disorders of pregnancy (HDP), including preeclampsia, gestational hypertension, and chronic hypertension, is essential for both clinical management and research. The Swedish Pregnancy Register automatically retrieves diagnostic codes based on the Swedish version of the International Classification of Diseases 10th revision (ICD-10), as recorded in antenatal, obstetric, and neonatal electronic medical records. The aim of the study was, for the first time, to assess the validity of HDP diagnoses within the Swedish Pregnancy Register in a contemporary population. MATERIAL AND METHODS: A multicenter validation study of women with deliveries from 2021 to 2023 who participated in the prospective Swedish study for Improving Maternal Pregnancy And Child ouTcomes (IMPACT) cohort. Women with a HDP diagnosis in the Swedish Pregnancy Register were retrospectively validated through standardized reviews of electronic medical records. The gold standard for classification followed the Swedish guidelines from the Swedish Society of Obstetrics and Gynecology (SFOG), updated in 2019. Incidence, sensitivity, and positive predictive value (PPV) were calculated and reported with 95% confidence intervals (CIs), using the Wilson score method. In addition, the study includes a descriptive analysis of preeclampsia disease characteristics and clinical diagnostic practices. RESULTS: Among 7443 women included in the validation study, 843 (11.3%, 95% CI 10.6-12.1) had a HDP diagnosis recorded in the Swedish Pregnancy Register and underwent validation. Within the study population, the register-based incidence of preeclampsia was 5.0% (95% CI 4.5-5.5%), while the minimum validated incidence was 5.1% (95% CI 4.6-5.6). The positive predictive value (PPV) of register diagnoses was 79.0% (95% CI 74.5-82.8%) for preeclampsia, 72.8% (95% CI 68.2-76.9%) for gestational hypertension, and 49.3% (95% CI 38.3-60.4%) for chronic hypertension, yielding an overall PPV for any hypertensive disorder of pregnancy diagnosis of 73.4% (95% CI 70.3-76.3%). Among validated cases of preeclampsia, 78% had proteinuria and the remaining cases were classified as preeclampsia based on other organ dysfunctions. CONCLUSIONS: In this contemporary Swedish cohort, a diagnosis of preeclampsia recorded in the Swedish Pregnancy Register demonstrated good validity, comparable to that reported in previous Nordic register validation studies.