Variations in prevalence of hyperemesis gravidarum by country of birth: A study of 900,074 pregnancies in Norway, 1967—2005

Abstract

Objective: To estimate the prevalence of hyperemesis gravidarum (HG) in women living in Norway by their country of birth, and explore whether the variations in the occurrence of HG could be explained by the differences in maternal sociodemographic factors. Design: This was a cross-sectional study. Methods: All primiparous women registered in the Medical Birth Registry of Norway (MBRN) from 1967 through June 2005 (N=900,074) comprised the sample. Data on HG, age, plurality and sex of the fetus were obtained from the MBRN and linked to the data on country of birth and maternal education obtained from Statistics Norway. Independent associations between country of birth and HG were studied by multiple logistic regression with and without adjustment for potential confounders. Results: The overall prevalence of HG in primiparous women in Norway during the study period was 0.89% (95% confidence interval (CI) 0.88—0.92). Women born in Western Europe had the lowest prevalence of HG (0.8%), whereas those born in India and Sri Lanka had the highest (3.2%). Women born in Africa (except North Africa) and India or Sri Lanka were 3.4 (95% CI 2.7— 3.5) and 3.3 (95% CI 2.6—3.4) times more likely to develop HG than women born in Norway, after adjustment for potential confounders. Conclusions: Substantial variations in the prevalence of HG in Norway by country of birth cannot be explained by the differences in maternal sociodemographic factors.