Measuring the invisible: perinatal health outcomes of unregistered women giving birth in Belgium

Background Research on the perinatal health of women without legal residence remains limited. We aimed to describe the sociodemographic profiles of women who were not registered in the Belgian National Population Registry, and to analyse the associations of registration status with pregnancy outcomes. Methods We analysed data from birth and death certificates linked with the National Population Registry for all singleton births between 2010 and 2016 (n = 871 283). With logistic regression we estimated the odds ratios for the associations between three perinatal outcomes and maternal registration status, stratified by nationality and adjusted for socioeconomic status. Results Mothers not legally residing in Belgium represented 1.9% of births. Unregistered women from newer EU member states and non-European countries were socioeconomically disadvantaged. Except for women with South American nationality, all other unregistered groups had higher rates of prematurity, low birthweight, and perinatal mortality, compared to registered mothers (p < 0.0001). Unregistered women from Belgium and EU15 countries had higher rates of prematurity, low birthweight, and perinatal mortality, even after adjustment for socioeconomic status (p < 0.0001). In contrast, the excess perinatal mortality in unregistered non-European mothers was partly attributed to their precarious socioeconomic situation. Conclusions Unregistered women giving birth in Belgium are socioeconomically heterogeneous, with some living in Belgium (undocumented) and others abroad. Overall, unregistered women had increased risks of adverse perinatal outcomes, but the causal mechanisms probably differ starkly between Belgians, Europeans and non-Europeans; further research is needed to understand these accrued rates. Studying the populations “invisible” in national statistics is important to identify the groups in most need of integration and access to services. Key messages Unregistered women were a heterogenous group with increased risks of adverse perinatal outcomes. Unregistered women from non-EU countries were presumably undocumented migrants. Their accrued rates of adverse outcomes were partly, but not entirely, explained by their worse socioeconomic situation.