The prevalence of pre-eclampsia in migrant relative to native Norwegian women: a population-based study

ObjectiveTo compare the prevalence of pre-eclampsia in migrant women with Norwegian women, and to study the prevalence of pre-eclampsia by length of residence in Norway. DesignObservational study. SettingThe Medical Birth Registry of Norway. PopulationAll Norwegian, Pakistani, Vietnamese, Somali, Sri Lankan, Filipino, Iraqi, Thai and Afghan women who gave birth after 20weeks of gestation during the period 1986-2005 in Norway. MethodsThe prevalence of pre-eclampsia was calculated by country of birth. The association of country of birth and length of residence in Norway with pre-eclampsia was estimated as the odds ratio (OR) with 95% confidence interval (CI), using Norwegian women as a reference. We made adjustments for maternal age, parity, multifetal pregnancy, year of delivery and maternal diabetes in multivariable analysis. Main outcome measurePre-eclampsia. ResultsMigrant women had a lower prevalence of pre-eclampsia than Norwegian women (2.7% versus 3.7%, P<0.001). Vietnamese (OR, 0.36; CI, 0.29-0.45), Afghan (OR, 0.52; CI, 0.30-0.90) and Thai (OR, 0.57; CI, 0.45-0.73) women had the lowest risk of pre-eclampsia relative to Norwegian women. Adjustment for the variables above or separate analyses for nulliparous women did not change the estimates notably. Using Norwegian women as the reference, the risk of pre-eclampsia increased by length of residence for migrant women: adjusted OR of 0.64 (0.59-0.70) at <5years and 0.91 (0.84-0.99) at 5years of residence. ConclusionsThe risk of pre-eclampsia was lower in migrants relative to Norwegian women, but increased by length of residence in Norway.