Substantial decrease in preeclampsia prevalence and risk over two decades: A population-based study of 1,153,227 deliveries in Norway

Objectives: Analyze secular trends of preeclampsia in Norway based on risk factors. Study design: Population-based cohort study of 1,153,227 women using data from Medical Birth Registry of Norway from 1999 to 2018. Aggregated data from Norwegian Prescription Database from 2004 to 2018 were used. Main exposure variable was time period. Descriptive statistics identified the prevalence of preeclampsia, labor induction and aspirin use. Multiple logistic regression analysis was performed to estimate the risk of preeclampsia during the time periods. Main outcome measures: Preeclampsia. Results: Overall preeclampsia prevalence decreased from 4.3% in 1999-2002 to 2.7% in 2015-2018. A reduction was observed in all subgroups of women with known risk factors (age, nulliparity, diabetes, chronic hypertension, assisted reproduction, twin pregnancy). Adjusted risk of preeclampsia was reduced by 44% from 1999-2002 to 2015-2018 (aOR = 0.56, 95%CI 0.54, 0.58), while the net prevalence of gestational hypertension remained stable over the study period. Labor induction increased 104%. Aspirin prescriptions increased among fertile women in the general Norwegian population. Conclusions: Preeclampsia prevalence and risk were reduced regardless of risk factors and despite an increased proportion of high-risk parturients (advanced age, lower parity, use of assisted reproduction). A corresponding increase in aspirin prescriptions among fertile women and an overall increase in labor inductions were also observed, suggesting that clinical interventions may partly explain the observed reduction in preeclampsia prevalence. Lower average blood pressure and improved health in the population may also explain some of the reduction.

Automated summary

The prevalence and risk of preeclampsia have decreased in Norway, regardless of risk factors. There has been an increase in labor inductions and the prescription of aspirin among fertile women.