Social inequalities in preterm birth in Scotland 1980-2003: findings from an area-based measure of deprivation

Objective The preterm birth rate in Scotland has been increasing in recent years. Although preterm birth rates show a social gradient, it is unclear how this gradient has been affected by the overall increase. We examined time trends in singleton live preterm birth rates in relation to area-based socio-economic indicators. Design Population-based retrospective cohort study. Setting Scotland. Participants All singleton live births delivered in Scottish hospitals between 1980 and 2003 (n = 1 423 993). Main outcome measures Singleton live preterm birth rates in each deprivation quintile were derived. Subgroup analyses of those born moderately preterm (32-36 weeks), very preterm (28-31 weeks) and extremely preterm (24-27 weeks) were performed. Results The rate of singleton live preterm births increased from 49.7 per 1000 live births in the 5-year period 1980-84 to 56.1 per 1000 in the 4-year period 2000-03, a relative increase of 12.9%. A marked social gradient was apparent at all time periods: relative indices of inequality were 1.63 (95% CI 1.38-1.92) in 1980-84 and 1.55 (1.44-1.66) in 2000-03. Similar social gradients existed for all gestational age subgroups. Smoking status at first antenatal contact and increased obstetric intervention, possibly reflecting improvements in fetal monitoring and neonatal care, appeared to explain some but not all the social gradient. Conclusions Social inequalities in preterm birth were apparent in Scotland between 1980 and 2003. In addition to helping pregnant women to stop smoking, other means to reduce social inequalities are required.