The immigrant paradox refers to the contrasting observations that immigrants usually experience similar or better health outcomes than the native-born population despite socioeconomic disadvantage and barriers to health care use. This paradox, however, has not been examined simultaneously in relation to varying degrees of exposure to the receiving society and across multiple outcomes and risk factors. To advance knowledge on these issues, we analysed data of the Maternity Experiences Survey, a nationally representative cross-sectional survey of 6421 Canadian women who delivered singleton infants in 2006-07. We compared the prevalence of adverse pregnancy outcomes and related risk factors according to women's ethnicity and time since migration to Canada. We calculated prevalences and prevalence ratios (PR) with 95% confidence intervals. Compared to Canadian-born women of European descent, recent immigrants were at lower risk of preterm delivery and morbidity during pregnancy despite having the highest prevalence of low income and low support during pregnancy among all groups, but the paradox was not observed among immigrants with a longer stay in Canada. In contrast, recent immigrants were at higher risk of postpartum depression. Immigrants of non-European origin also had higher prevalence of postpartum depression, irrespective of their length of residence in Canada, but immigrants from European-origin countries did not. Exposure to Canada was also positively associated with higher alcohol and tobacco consumption and body mass index. Canadian-born women of non-European descent were at higher risk of preterm birth and hospitalisation during pregnancy than their European-origin counterparts. Our findings suggest that the healthy migrant hypothesis and the immigrant paradox have limited generalisability. These hypotheses may be better conceptualised as outcome-specific and dependent on immigrants' ethnicity and length of stay in the receiving country.
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