The influence of maternal childhood and adulthood social class on the health of the infant
Introduction
Applying a life course perspective to social inequalities in health implies expanding the focus from the most immediate causes of inequality to those further back in time, considering childhood and even intra-uterine life. It is well documented that both social and health-related factors in early life affect both social status and health in adulthood, and these are in turn interrelated and constitute what has traditionally been the main focus in the field of health inequalities (Hardy & Kuh, 2002; Kuh & Ben-Shlomo, 2004). The interactions of these factors are complex, and things sometimes thought to be important as direct risks of adverse health outcomes—such as smoking—might, for example, be more important among teenagers as a step in a social career, where the more important determinants of adult health are in the continuation of this career (Koivusilta, Rimpela, Rimpela, & Vikat, 2001). Early life may of course affect adult health in very direct ways, as has been suggested in the theory of biological programming of the foetus (Barker, 1991). However, it has been shown that social circumstances in both childhood and adulthood might also affect the impact of early health-related problems such as perinatal stress on adult health (Power & Hertzman, 1997). Social factors in childhood and adult life have also been shown to be of varying importance for different causes of death. Stomach cancer, for example, seems more strongly related to childhood, and lung cancer to adulthood social conditions, whereas CHD risks seems to be affected by social circumstances during the entire life course (Davey Smith, Gunnell, & Ben-Shlomo, 2001). The life course perspective on health has been applied to women to a lesser extent than to men, and this has been suggested as an important challenge for the field (Bartley, Sacker, & Schoon, 2002).
To study a woman's life course and the infant is taking yet another step: another individual is involved and we must start thinking intergenerationally. How might social conditions over the life course of a woman affect the health of her infant? Social inequalities in infant health are a universal phenomenon, found even in the more equal societies such as the Nordic countries (Arntzen & Nybo Andersen, 2004; Gisselmann, 2005). Indicators such as socio-economic status, income and education generally show that more disadvantaged social groups have higher rates of low birth weight infants and infant mortality.
It has been suggested that work-related exposures increase the risk of preterm birth (Mozurkewich, Luke, Avni, & Wolf, 2000) and impaired foetal growth (Seidler et al., 1999), important risk factors for both low birth weight and infant mortality. It has been suggested that psychosocial factors might prove to be important mediators for social inequalities in preterm birth, although more research is needed to clarify the mechanisms (Kramer, Seguin, Lydon, & Goulet, 2000). There are relevant behavioural factors: diet, exercise, smoking and consumption of alcohol and drugs. Smoking, the use of drugs and a high alcohol intake are more prevalent in groups with lower social status, while the intake of important micronutrients is lower. Of these factors, smoking is probably most important (Kramer et al., 2000), increasing the risk for both low birth weight and infant mortality.
In relation to the determinants of social inequalities in infant health, the focus has been on maternal factors in adulthood, and earlier maternal social circumstances seem largely unexplored. However, the mediators mentioned above in relation to adult social class are not independent of social background. The foundations of many psychosocial characteristics are laid in childhood, a time when the individual learns how and how not to deal with problems and stress. Those with a working class background are more likely to experience more difficulties during childhood, and this seems to be combined with a worse ability to handle these difficulties (Kristenson, Eriksen, Sluiter, Starke, & Ursin, 2004). Education is strongly related to childhood social class, which will later be a determining or limiting factor for the kind of job obtained, thereby affecting job exposure. Attitudes and behaviours related to food, exercise and smoking are also established in childhood, but it seems unclear as to how much this affects behaviour in adult life. Studies show a greater impact of adult class, indicating that behaviour changes with change of class, so that this explains only a small part of adult health inequalities (Karvonen, Rimpela, & Rimpela, 1999; Mishra, Prynne, Paul, Greenberg, & Bolton-Smith, 2004; van de Mheen, Stronks, Looman, & Mackenbach, 1998).
Maternal health in itself, in relation to infant health, is seldom mentioned in the study of social inequalities in infant health in the developed world, unless it concerns specific health problems such as gestational hypertension. However, social differences during pregnancy and birth are not only likely to affect social inequalities in infant health through specific health problems, but also through the entire social health gradient. We know how interlinked social and health careers are, and health risks are accumulated throughout the life course. Differences in health-related behaviour have been shown to be present beginning in the early teenage years (Koivusilta, Rimpela, & Vikat, 2003), and social inequalities in health by own social class have been shown to be present from the age of 20 (Rahkonen, Arber, & Lahelma, 1995). Moreover, studies show remarkable consistency in the way that social and biological factors are associated with social mobility. Those who are upwardly mobile have more advantageous and the downwardly mobile less advantageous outcomes, than those who are stable (Blane, Smith, & Hart, 1999; Illsley, 1955).
In this study, we consider the mother as the starting point. She also will be affected by the circumstances of her parents from the moment of conception. Even a biological factor such as her birth weight can be seen as the result of social conditions, perhaps from several generations back, in itself a cumulative indication of development up to the time of measurement (Morton, 2004).
In sum, we may view a young woman largely as a product of her parents’ social environment. She has grown up knowing a class-based norm system, entailing health-related attitudes and behaviours. Reaching adult age, she has been affected by her social circumstances from birth and onward, and these may affect her infant through her social norms and behaviours, her biological body (accumulated health) before childbirth and after (if breast feeding). Thus, the question is: how is infant health affected by maternal childhood class and adult social class? This seems to be a largely unexplored area of research. Considering the timeline from the birth of the mother to the first year of her infant's life also raises the question of whether the association with social class is greater closer to the birth of the infant. These are the empirical questions posed in this paper.
Section snippets
Data and method
For women born 1946–1960, it was possible to retrieve information on childhood class from the 1960 census. Linkages were made to the 1970, 1980 and 1985 censuses for information on the women's adult life. From the medical birth register, information was retrieved on all infants born to these women 1973–1990. All infant deaths were used as the numerator and the infants in a 10% representative sample of the rest (sampling due to reasons of anonymity) were used to estimate the denominator. The
Results
Table 4 shows that childhood and adulthood social class of the mothers were both associated with all outcomes, and when mutually adjusted, childhood class was still significant for low birth weight and neonatal mortality.
Manual maternal childhood class was consistently associated with higher odds ratios for low birth weight and neonatal mortality (OR ranging between 1.09 and 1.17, all but one significant at ), and this was true for postneonatal mortality when adult social class was not in
Discussion
We conclude that the pattern of association of a woman's social class with the health of her infant is clear: social class, adult class more than childhood class, is important for the size of health inequalities. The results for low birth weight and neonatal mortality indicate that the influence of childhood class is in fact greater than the association of childhood class with adult class, to our knowledge a new finding.
Acknowledgements
The author wishes to thank Örjan Hemström, Ilona Koupil and Denny Vågerö for helpful comments and suggestions.
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