Relation-ship in Spain of the Length of the Gestation and the Birth Weight with Mother's Nationality during the Period 2001-2005

Background: Association between immigration and low birth weight (LBW) and preterm birth (PB) is an important indicator of health inequalities. The objective of this study is to analyse the differences between LBW and PB according to the mother's nationality in newborns in Spain. Methods: Data were provided from the National Statistical Bulletin of Birth of 1,878,718 newborns in the period 2001-2005. The nationality was considered the exposure variable (Spanish-Immigrant). The outcomes were LBW (<2,500 gr and >=37 gestational weeks) and PB (<37 gestational weeks). Odds ratios were calculated and adjusted by possible confounders by logistic regression. Results: PB and LBW prevalence were higher in Spanish women (7.9% and 3.2% respectively). In comparison with Spanish ones, the lowest risk of PB was observed in North Africa (ORa=0.77 CI95% 0.74-0.80). With respect to LBW, the lowest risk was found in mothers from South America (ORa=0.62 CI95% 0.59-0.65) and Eastern Europe (ORa=0.65 CI95% 0.60-0.71). Conclusion: Results of LBW and PB were more favourable in the births of immigrant women. It could be associated with the healthy migrant effect and a low frequency of risk practices during gestation.