Differences in low birth weight and preterm birth in Spanish and immigrants newborns

Background:  Although the association between immigration and low birth weight (LBW) and preterm birth (PB) is an important indicator of health inequalities, the studies in this topic are not conclusive. The objective of this study is to analyse the differences between low birth weight (LBW) and preterm birth (PB) according to the mother’s nationality in newborns in Spain.
Methods: Cross sectional study. Data were provided from the National Statistical Bulletin of Birth of 1,878,618 newborns in the period 2001-2005. The nationality was considered the exposure variable -Spanish- Immigrant and after regrouped by countries: Spain, Southern Europe, rest of Western countries (rest of countries in Western Europe, United States and Canada), Eastern Europe, North Africa, Sub-Saharan Africa, Central America and, Caribbean, South America, Asia and Oceania-. The outcomes were LBW (borns <2,500 gr with <=37gestational weeks) and PB (<37 gestational weeks). Crude and adjusted Odds ratios were calculated by means of logistic regression.
Results: PB and LBW prevalence were higher in Spanish women (7.9% and 3.2% respectively). By country groups, the highest prevalence of PB was found in Southern Europe (8.8%) and LBW in Sub-Saharan Africa (4.6%). In comparison with Spanish ones, the lowest risk of PB was observed in North Africa (OR= 0.77 CI_95% 0.74-0.80). With respect to LBW, the lowest risk was found in mothers from South America (OR=0.62 CI_95% 0.59-0.65) and Eastern Europe (OR=0.65 IC_95% 0.60-0.71) and the highest one in births of Sub-Saharan mothers (OR=1.44 IC_95% 1.30-1.60).
Conclusion: Although the birth outcomes (LBW and PB) were more favorable in births from foreign women, the results of this study suggest that certain groups have differences in the risk of LBW and PB depending of factors related with the country-origin. It could be associated with the healthy migrant effect and a low frequency of risk practices during gestation.