The association of maternal country of birth and education with hypertensive disorders of pregnancy: A population-based study of 960516 deliveries in Norway

IntroductionPrevious studies estimating the association of maternal country of birth and education with hypertensive disorders of pregnancy (HDP) have shown conflicting results. The aim of the study was to assess the prevalence of HDP and estimate the association of maternal country of birth and education level with preeclampsia/eclampsia and gestational hypertension in Norway. Material and methodsWe performed a population-based observational cohort study linking two population datasets: The Medical Birth Registry of Norway and Statistics Norway (SSB). Singleton deliveries in Norway between 1999 and 2014 (907048 deliveries) were stratified by parity. Multiple regression analysis was performed. ResultsIn 20% of the deliveries the woman was born outside of Norway. Foreign-born women had lower risk of preeclampsia/eclampsia and gestational hypertension compared with Norwegian-born women. High education reduced the risk for preeclampsia/eclampsia by 34% (adjusted odds ratio 0.66, 95% CI 0.62-0.69), compared with women with secondary education among nulliparous women, and by 39% (adjusted odds ratio 0.61, 95% CI 0.57-0.65) among parous women. Poorly educated women had no increased risk of HDP compared with women with secondary education. Among highly educated nulliparous women the risk of preeclampsia/eclampsia was lower but the risk of gestational hypertension higher compared with women of similar parity with secondary education. Adjustment for confounding variables had minimal effect on these estimates. ConclusionsMaternal country of birth and education were associated with HDP. Women with higher education had the lowest risk of HDP, and Norwegian-born women had the highest risk of HDP, regardless of parity and other confounding factors.