Commentary: Social inequalities in risk of stillbirth—the price of success?

Anne-Marie Nybo Andersen

Department of Social Medicine, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark. E-mail:a.nybo{at}socmed.ku.dk

The issue of socially determined health inequalities has been on the public health research agenda since the Black Report. An overwhelming amount of research has shown that socially patterned inequality in health exists for most diseases and causes of death, even within developed countries,1 and several studies indicate that the differentials seem to increase over time, despite political intentions of reducing health inequalities.2

This has led to a growing awareness of the need for explanations rather than description.3 It is questionable whether the understanding and explanation of social inequality in health can be found exclusively within the discipline of epidemiology, especially if the search for explanations means looking for mediating risk factors, although this approach may make a valuable contribution. For example, in a study of social class differences in lung cancer mortality, the social difference was fully explained by including lung health, material well-being and early life indicators in addition to smoking and age.4

Stephansson and colleagues have investigated the influence of occupational status on the risk of stillbirth in Sweden and have attempted to explain the social differential by including a variety of potential mediating risk factors using population-based register data and individual hospital records.5 They found a strong social gradient in risk of stillbirth, especially in term antepartum stillbirths and intrapartum stillbirths, but failed to explain this gradient from the available data on risk factors.

The social gradient might be ‘explained’—at least to some extent—by including numerous individual risk factors in the model (if available), but a population-level approach might also be useful in the search for explanations.6

The time trends in the social gradients in stillbirth are difficult to study because of variations in the social classifications over time, but might give additional information. A study on perinatal mortality, using data covering the 1930s and covering the same region in Sweden as Stephansson's study, showed that while the risk of stillbirth was much higher, the relative differences between the social groups appeared smaller than those found in the recent material.7 Comparison of the social gradients published in the present paper with those published for Swedish data from the time period 1985–19868 indicate an increase in social inequality in stillbirth risk in recent years, and these data should be comparable.

Also, looking at variations between countries might be useful. Reading the paper one should bear in mind that Sweden has the lowest stillbirth rate in the world (3.5 per 1000 births), compared to stillbirth rates of 7.5/1000 births in British Colombia, Canada (1999), 6.7/1000 births in Ireland (1998), around 6/1000 births in UK (1996) and more than 20/1000 births in most African countries.

It might be useful as well to make comparisons of stillbirth rates in the three Scandinavian countries, since the three societies are egalitarian, have homogeneous populations, and comparable health care systems (including antenatal care) and health registration systems. The stillbirth rates in Norway and Denmark, when looked at in an international context, are low, 4.2 and 4.6 per 1000 births respectively, but substantially higher than that of Sweden.9 These differences still remain to be explained, but the fact that Danish and Norwegian women have the highest smoking prevalences in the world is an indication of differences in health-related behaviour. Interestingly, published data indicate that the social gradient in stillbirth risk is lower in Norway than in Sweden,10 and non-existent in Denmark.11

Studies outside the field of perinatal epidemiology indicate a widening social gap together with an overall decrease in disease occurrence. This has been most convincingly demonstrated for coronary heart disease12,13 but it is also evident in the completely different field of dental health,14,15 and it might well be so in other areas of overall success for public health.

Sweden has succeeded in lowering the stillbirth rate. We do not know exactly how and why, but we would like to give credit to a well-functioning public health care system, including both the birth care institution and the antenatal care programme, and general disease prevention initiatives in society (e.g. anti-smoking and anti-alcoholism policies). In this light, the findings published by Stephansson and colleagues of a strong social gradient in stillbirth risk and an even stronger gradient in intra-partum stillbirths are discouraging. However, the fact that the social gradient in stillbirth risk is inversely related to overall risk—at least in Scandinavia—could raise the heretical question: does the success of preventive medicine have a price to pay—that of increasing social inequality in health?

References

1 Kunst AE, Groenhof F, Mackenbach JP, Health EW. Occupational class and cause specific mortality in middle aged men in 11 European countries: comparison of population based studies. EU Working Group on Socioeconomic Inequalities in Health. Br Med J 1998;316:1636–42.[Abstract/Free Full Text]

2 Acheson DC. Independent Inquiry into Inequalities in Health. London: The Stationery Office, 1998.

3 Blane D. Commentary: Socioeconomic health differentials. Int J Epidemiol 2001;30:292–93.[Free Full Text]

4 Hart C, Hole D, Gillis C, Davey Smith G, Watt G, Hawthorne V. Social class differences in lung cancer mortality: risk factor explanations using two Scottish cohort studies. Int J Epidemiol 2001;30:268–74.[Abstract/Free Full Text]

5 Stephansson O, Dickman PW, Johansson ALV, Cnattingius S. The influence of socioeconomic status on stillbirth risk in Sweden. Int J Epidemiol 2001;30:1296–301.[Abstract/Free Full Text]

6 Pearce N. Epidemiology as a population science. Int J Epidemiol 1999; 28:S1015–18.[ISI][Medline]

7 Thorén S. Om den Perinatala Dödlighetens Förändringar i Sverige under de Seneste Decennierna (On the variations in perinatal mortality in Sweden during the last decades). Stockholm: Karolinska Institute, 1948.

8 Haglund B, Cnattingius S, Nordstrom ML. Social differences in late fetal death and infant mortality in Sweden 1985–86. Paediatr Perinat Epidemiol 1993;7:33–44.[Medline]

9 Health Statistics in the Nordic Countries 1999. Copenhagen: NOMESCO, 2001.

10 Arntzen A, Magnus P, Bakketeig LS. Different effects of maternal and paternal education on early mortality in Norway. Paediatr Perinat Epidemiol 1993;7:376–86.[Medline]

11 Olsen O, Madsen M. Effects of maternal education on infant mortality and stillbirths in Denmark. Scand J Public Health 1999;27:128–36.[ISI][Medline]

12 Tuchsen F, Endahl LA. Increasing inequality in ischaemic heart disease morbidity among employed men in Denmark 1981–1993: the need for a new preventive policy. Int J Epidemiol 1999;28:640–44.[Abstract]

13 Barnett E, Armstrong DL, Casper ML. Evidence of increasing coronary heart disease mortality among black men of lower social class. Ann Epidemiol 1999;9:464–71.[ISI][Medline]

14 Truin GJ, Konig KG, Bronkhorst EM, Frankenmolen F, Mulder J, van't Hof MA. Time trends in caries experience. Caries Res 1998;32:1–4.[ISI][Medline]

15 Antoft P, Rambusch E, Antoft B, Christensen HW. Caries experience, dental health behaviour and social status—three comparative surveys among Danish military recruits in 1972, 1982 and 1993. Community Dent Health 1999;16:80–84.[ISI][Medline]