Factors determining the variation in birth weight in Spain (1980-2010)

Background: Low weight and premature deliveries arouse clinical interest concerning the survival of newborns. The determinants of birth weight among Spanish natives and immigrants may differ. Research which considers maternal origin and associated factors such as age and parity is important. Aim: This study analyses and models the influence of the rapid and intense arrival of immigrants in Spain on birth weight variation. Method: Data on deliveries from the Spanish National Institute for Statistics (n = 9 443 882) are analysed regarding low birth weight, premature births and other variables. The inter-relation among these variables was interpreted by means of logistic regression models. Results and conclusions: The birth weight has decreased since 1980 in Spain, but has slightly recovered in recent years. Meanwhile the percentage of foreign maternities increased to 17.3% in 2010. Logistic regression models assess the different influence of variables known to determine low birth weight (weeks of gestation, sex, etc.) and other maternal characteristics (age at delivery, professional activity, etc.). The progressively greater contribution of foreign women to total births in Spain and their differential numerical input to the various risk groups have slowed the pattern of reduction in the mean weight of newborns in this country