Socio-economic disparities in pregnancy outcome: why do the poor fare so poorly?

In this paper, we review the evidence bearing on socio-economic disparities in pregnancy outcome, focusing on aetiological factors mediating the dispa rities in intrauterine growth restriction (IUGR) and preterm birth. We firs t summarise what is known about the attributable determinants of IUGR and p reterm birth, emphasising their quantitative contributions (aetiological fr actions) from a public health perspective. We then review studies relating these determinants to socio-economic status and, combined with the evidence about their aetiological fractions, reach some tentative conclusions about their roles as mediators of the socio-economic disparities. Cigarette smok ing during pregnancy appears to be the most important mediating factor for IUGR, with low gestational weight gain and short stature also playing subst antial roles. For preterm birth, socio-economic gradients in bacterial vagi nosis and cigarette smoking appear to explain some of the socio-economic di sparities; psychosocial factors may prove even more important, but their ae tiological links with preterm birth require further clarification. Research that identifies and quantifies the causal pathways and mechanisms whereby social disadvantage leads to higher risks of IUGR and preterm birth may eve ntually help to reduce current disparities and improve pregnancy outcome ac ross the entire socio-economic spectrum.