Are all immigrant mothers really at risk of low birth weight and perinatal mortality? The crucial role of socio-economic status.

BACKGROUND Increasing studies show that immigrants have different perinatal health outcomes compared to native women. Nevertheless, we lack a systematic examination of the combined effects of immigrant status and socioeconomic factors on perinatal outcomes. Our objectives were to analyse national Belgian data to determine 1) whether socioeconomic status (SES) modifies the association between maternal nationality and perinatal outcomes (low birth weight and perinatal mortality); 2) the effect of adopting the Belgian nationality on the association between maternal foreign nationality and perinatal outcomes. METHODS This study is a population-based study using the data from linked birth and death certificates from the Belgian civil registration system. Data are related to all singleton births to mothers living in Belgium between 1998 and 2010. Perinatal mortality and low birth weight (LBW) were estimated by SES (maternal education and parental employment status) and by maternal nationality (at her own birth and at her child's birth). We used logistic regression to estimate the odds ratios for the associations between nationality and perinatal outcomes after adjusting for and stratifying by SES. RESULTS The present study includes, for the first time, all births in Belgium; that is 1,363,621 singleton births between 1998 and 2010. Compared to Belgians, we observed an increased risk of perinatal mortality in all migrant groups (p < 0.0001), despite lower rates of LBW in some nationalities. Immigrant mothers with the Belgian nationality had similar rates of perinatal mortality to women of Belgian origin and maintained their protection against LBW (p < 0.0001). After adjustment, the excess risk of perinatal mortality among immigrant groups was mostly explained by maternal education; whereas for sub-Saharan African mothers, mortality was mainly affected by parental employment status. After stratification by SES, we have uncovered a significant protective effect of immigration against LBW and perinatal mortality for women with low SES but not for high SES. CONCLUSIONS Our results show a protective effect of migration in relation to perinatal mortality and LBW among women of low SES. Hence, the study underlines the importance of taking into account socioeconomic status in order to understand more fully the relationship between migration and perinatal outcomes. Further studies are needed to analyse more finely the impact of socio-economic characteristics on perinatal outcomes.