Spontaneous very preterm birth in relation to social class, and smoking: a temporal-spatial analysis of routinely collected data in Aberdeen, Scotland (1985-2010)

Objective To examine trends of spontaneous very preterm birth (vPTB) and its relationship with maternal socioeconomic status and smoking. Methods This was a population-based cohort study in Aberdeen Maternity Hospital, UK. The cohort was restricted to spontaneous singleton deliveries occurring in Aberdeen from 1985 to 2010. The primary outcome was very preterm birth which was defined as <32 weeks gestation and the comparison group was deliveries >= 37 weeks of gestation. The main exposures were parental Social Class based on Occupation, Carstairs' deprivation index and smoking during pregnancy. Logistic regression was used to estimate the association between vPTB and the exposures. Results There was an increased likelihood of vPTB in those with unskilled-occupations compared to professional-occupations [aOR:2.77 (95%CI:1.54-4.99)], in those who lived in the most deprived areas compared to those in the most affluent [aOR: 2.16 (95% CI: 1.27-3.67)] and in women who smoked compared to those who did not [aOR: 1.74 (95% CI: 1.36-2.21)]. The association with Carstairs index was no longer statistically significant when restricted to smokers but remained significant when restricted to non-smokers. Conclusion The strongest risk factor for vPTB was maternal smoking while socioeconomic deprivation showed a strong association in non-smokers. Smoking cessation interventions may reduce vPTB. Modifiable risk factors should be explored in deprived areas.