Differences in perinatal health between immigrant and native-origin children: Evidence from differentials in birth weight in Spain

1. The relevance of birth weight, and its determinants in the Spanish contextBirth weight has been the object of extensive research in various fields of scientific enquiry, from medicine to social epidemiology, sociology, and demography. The study of the adverse consequences of unhealthy weights at birth (4,000/4,500 grams) has mainly focused on health and educational outcomes. Because of the huge amount of evidence linking Low Birth Weight (LBW) to adverse health and cognitive outcomes, social epidemiology has tried extensively to assess the prevalence of LBW in different settings and different subsamples of the population (see, for instance, Reichman 2005, Teitler et al. 2007, Buekens et al. 2013). Although scholars have traditionally privileged the study of Low Birth Weight (LBW), research on High Birth Weight (HBW) is gaining momentum. In this review we briefly summarize both the determinants and consequences of deviation from healthy weights.On the one hand, the World Health Organisation defines LBW as less than 2,500 grams, irrespective of the gestational age of the infant. In the specialized literature it is interpreted as one of the most straightforward indicators of perinatal health and of infant health more generally. According to the American Academy of Paediatrics, LBW has different origins, ranging from the most obvious - those associated with genetic factors (foetal chromosomal abnormalities), the mother's health (high blood pressure, heart or kidney disease), and the mother's lifestyle (incorrect nutrition during gestation, smoking, and the consumption of other substances) - to problems with the development of the placenta (intra-amniotic infection, placental abruption, and placental insufficiency). LBW correlates with infant morbidity and mortality. Smaller babies are more likely to experience severe health risks after birth, and the effects of this early disadvantage are long-lasting: they are more prone to report general worse health later in life (Johnson and Schoeni 2007) and to suffer from a higher incidence of specific conditions such as diabetes, asthma, coronary disease, metabolic syndrome, and high blood pressure (Barker 1995, Johnson and Schoeni 2011). The negative impact of LBW on cognitive development and educational outcomes (Hack et al. 1995) has been shown to be similarly enduring. These children show poorer school readiness (Reichman 2005), evidence of increased school difficulties and hyperactivity until the age of 18 (McCormick et al. 1990), lower chances of completing high school at the standard age, lower educational attainment (Conley and Bennet 2000), and even lower earnings as adults (Black et al. 2007). However, socio-economic factors tend to mediate these relationships. Large differences in the incidence of LBW have consistently been reported across socio-economic groups in different countries (Kramer et al. 2000). Whereas more maternal resources . whether a higher educational level (Boardman et al. 2002), social class (Pattenden et al. 1999), or a supportive social and emotional climate (Hohmann-Marriott 2009) . all tend to improve birth outcomes, pregnancy later in life (Luke and Brown 2007) and non-marital birth (Castro-Martin 2010) are associated with an increased risk of LBW. Interestingly, according to the literature, in a number of affluent countries immigrant women tend to experience better birth outcomes than native women (see Guendelman et al. 1999), a result that will be discussed in the next section.Spain is no exception in this general picture. There are significant traces of inequality in perinatal health according to social background. Castro-Martin (2010) showed that the children of unmarried mothers suffer a higher risk of low birth weight, suggesting that the health disadvantage of children of non-marital couples is significant, even though recent social acceptance of non-marital unions and the selection of couples into this new form of cohabitation have helped to reduce it over time. …