Study cohorts

In this study we used two cohorts: one for the estimation of cumulative incidence of post-pregnancy hypertension and the other cohort for the estimation of hazard ratios for post-pregnancy hypertension.

Cumulative incidences of post-pregnancy hypertension—using the medical birth register, we identified all women with a first pregnancy lasting 20 or more weeks and ending in live birth or stillbirth between 1995 and 2012. We excluded women with any cardiac or circulatory system disorder (international classification of diseases, eighth revision (ICD-8), codes 390-458, or 10th revision (ICD-10) codes I00.0-I99.9) registered in the national patient register before their first delivery, and women with known or potential pregestational hypertension.

Hazard ratios for post-pregnancy hypertension—using the medical birth register, we identified all women who had at least one pregnancy that lasted 20 or more weeks and ended in live birth or stillbirth between 1978 and 2012, and who were living in Denmark at some point during the follow-up period, 1995-2012. We excluded women with any cardiac or circulatory system disorder registered in the national patient register before their first delivery or before 1995, whichever came later, and women with known or potential pregestational hypertension.