Scottish Longitudinal Study
Development & Support Unit

Current Projects

Project Title:

From Birth to Childhood: investigating socio-economic differences in health trajectories via administrative data

Project Number:

2013_008

Researchers:

Bianca DeStavola (Pathways, LSHTM)
Emily Grundy (Pathways, University of Cambridge)
Richard Silverwood (Pathways, LSHTM)
Chris Dibben (University of St Andrews)
Lee Williamson (University of St Andrews)

Start Date:

3 September 2013

Summary:

Infant mortality is strongly patterned by socio-economic conditions, even in developed countries.(1) It is also strongly and negatively related to birthweight, with the gradient seen even in babies born at term.(2) This suggests that birthweight, itself strongly patterned by socio-economic status,(3-4) may act as a mediator in the pathway by which socio-economic disadvantage leads to increasing risk of infant death. However, there is also evidence that shows that the risks associated with low birthweight vary between population subgroups in apparently counterintuitive ways. The most striking example of this comes from babies born to mothers who smoked during pregnancy.(5) Such babies are usually around 100-200g lighter at birth than babies of non-smoking mothers, yet, for a given low birthweight, those exposed to maternal smoking are at lower risk of infant mortality than those unexposed. Similar contradictory patterns emerge from observations on babies born to migrants or ethnically disadvantaged groups.(6-7) In each of these cases, the low birthweight babies in subgroups with greater prevalence of low birthweight, the “disadvantaged”, experience lower infant mortality rates than low birthweight babies in more advantaged groups.

This “low birthweight paradox” has received much attention in the literature.(5,7-9) Two broad alternative explanations have been offered. The first assumes that birthweight modifies the effect of disadvantage on infant mortality; the second that birthweight has no direct effect on infant mortality but shares a confounder with the outcome.(8) The discussion regarding which of these two explanations is the more plausible is ongoing.(10-11)

The existing Pathways programme includes a project focussed on elucidating the mediatory role of birthweight in the association between social disadvantage and infant mortality using the England and Wales ONS Longitudinal Study (LS). Using the SLS we will be able to extend this research to investigate a much wider range of health outcomes (including obesity) and their potential social and biological determinants/mediators.

The proposed study will involve pioneering the use of child health record data linked to the SLS and will create usable measures from existing administrative records (by validating, combining, etc.) and therefore offer new validated tools to the broader research community.

The research brings together the methodological interests and expertise of the Pathways node with the richness of the SLS and linked databases, and expertise of the SLS group, to address a question of major policy interest – trajectories from very early life to childhood health and well-being.

We will examine health trajectories and outcomes of a cohort born 1991 to 2005. For all babies some information on the mothers’ circumstances prior to the birth is available from the Vital Events (VE) birth records as part of the SLS and the Scottish Morbidity Records (SMR) maternity dataset (SMR02). Additionally, Census information will provide the educational attainment and socio-economic characteristics of the parent(s). Birth weight is available from the SMR02 and detailed information on child, mother and other household members is available from linked health visitor and primary school health assessments at key points (ISD child health surveillance data). This holds, for example, information on smoking by the mother; feeding patterns in infancy; cognitive and social measures in early years and at school, and measures of growth including height and weight.

In using this data the research aim is to investigate socio-economic differences in health trajectories from birth to childhood. The existing Pathways programme includes a project focussed on elucidating the mediatory role of birthweight in the association between social disadvantage and infant mortality using the England and Wales ONS Longitudinal Study. Using the SLS we aim to extend this research to investigate a much wider range of health outcomes (including obesity) and their potential social and biological determinants/mediators.

The proposed study also aims to pioneer the use of child health record data linked to the SLS and to create usable measures from existing administrative records (by validating, combining, etc.) and therefore offer new validated tools to the broader research community.

References:

  1. Melve KK, Skjaerven R. Birthweight and perinatal mortality: paradoxes, social class, and sibling dependencies. International Journal of Epidemiology. 2003; 32(4): 625-32.

  2. Wilcox AJ. On the importance - and the unimportance - of birthweight. International Journal of Epidemiology. 2001; 30(6): 1233-41.

  3. Kramer MS, Seguin L, Lydon J, Goulet L. Socio-economic disparities in pregnancy outcome: why do the poor fare so poorly? Paediatric and Perinatal Epidemiology. 2000; 14(3): 194-210.

  4. Stephansson O, Dickman PW, Johansson AL, Cnattingius S. The influence of socioeconomic status on stillbirth risk in Sweden. International Journal of Epidemiology. 2001; 30(6): 1296-301.

  5. Wilcox AJ. Commentary: On the paradoxes of birthweight. International Journal of Epidemiology. 2003; 32(4): 632-3.

  6. Wilcox A, Russell I. Why small black infants have lower mortality rate than small white infants. The case for population specific standards for birthweight. Journal of Pediatrics. 1990; 116(1): 7-10.

  7. Wilcox AJ. Birth-weight and perinatal mortality. The effect of maternal smoking. American Journal of Epidemiology. 1993; 137(10): 1098-104.

  8. Hernandez-Diaz S, Schisterman EF, Hernan MA. The birth weight "paradox" uncovered? American Journal of Epidemiology. 2006; 164(11): 1115-20.

  9. Yerushalmy.J. Relationship of parents cigarette smoking to outcome of pregnancy. Implications as to problem of inferring causation from observed associations. American Journal of Epidemiology. 1971; 93(6): 443-56.

  10. Basso O, Wilcox AJ. Intersecting Birth Weight-specific Mortality Curves: Solving the Riddle. American Journal of Epidemiology. 2009; 169(7): 787-97.

  11. Basso O, Wilcox AJ, Weinberg CR. Birth weight and mortality: Causality or confounding? American Journal of Epidemiology. 2006; 164(4): 303-11

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