Socioeconomic inequality in birth weight and gestational age in Denmark 1996-2007: Using a family-based approach to explore alternative explanations

► Low socioeconomic position is known to be associated with increased risk of preterm birth and decreased birth weight. ► We explore the nature of this relationship by contrasting ordinary analyses with analyses where we compare children who are siblings and children who are first cousins. ► Our findings suggest that a major part of the association between maternal education and the outcomes may be explained by factors shared by mothers who are siblings.