Abstract
BackgroundThe literature shows a variable and inconsistent relationship between socioeconomic position and preterm birth. We examined risk factors for spontaneous and iatrogenic preterm birth, with a focus on socioeconomic position and clinical risk factors, in order to explain the observed inconsistency.MethodsWe carried out a retrospective population-based cohort study of all singleton deliveries in Nova Scotia from 1988 to 2003. Data were obtained from the Nova Scotia Atlee Perinatal Database and the federal income tax T1 Family Files. Separate logistic models were used to quantify the association between socioeconomic position, clinical risk factors and spontaneous preterm birth and iatrogenic preterm birth.ResultsThe study population included 132,714 singleton deliveries and the rate of preterm birth was 5.5%. Preterm birth rates were significantly higher among the women in the lowest (versus the highest) family income group for spontaneous (rate ratio 1.14, 95% confidence interval (CI) 1.03, 1.25) but not iatrogenic preterm birth (rate ratio 0.95, 95% CI 0.75, 1.19). Adjustment for maternal characteristics attenuated the family income-spontaneous preterm birth relationship but strengthened the relationship with iatrogenic preterm birth. Clinical risk factors such as hypertension were differentially associated with spontaneous (rate ratio 3.92, 95% CI 3.47, 4.44) and iatrogenic preterm (rate ratio 14.1, 95% CI 11.4, 17.4) but factors such as diabetes mellitus were not (rate ratio 4.38, 95% CI 3.21, 5.99 for spontaneous and 4.02, 95% CI 2.07, 7.80 for iatrogenic preterm birth).ConclusionsSocioeconomic position and clinical risk factors have different effects on spontaneous and iatrogenic preterm. Recent temporal increases in iatrogenic preterm birth appear to be responsible for the inconsistent relationship between socioeconomic position and preterm birth.
Highlights
The literature shows a variable and inconsistent relationship between socioeconomic position and preterm birth
A similar phenomenon was observed in New Zealand, where the strong socioeconomic gap in preterm birth rates observed in the 1980s disappeared by the turn of the century [7]
It is possible that spatial and temporal variations in the frequency of the preterm birth subtypes, namely, spontaneous preterm birth and iatrogenic preterm birth, or temporal changes in clinical risk factors for these subtypes of preterm birth underlie the vagaries of the socioeconomic position–preterm birth relationship
Summary
The literature shows a variable and inconsistent relationship between socioeconomic position and preterm birth. We examined risk factors for spontaneous and iatrogenic preterm birth, with a focus on socioeconomic position and clinical risk factors, in order to explain the observed inconsistency. Factors such as multi-fetal pregnancy, congenital malformations, older maternal age and race/ethnicity are strongly associated with preterm birth [1,2,3,4]. It is possible that spatial and temporal variations in the frequency of the preterm birth subtypes, namely, spontaneous preterm birth (following preterm labour) and iatrogenic preterm birth (following labour induction or cesarean delivery before labour onset), or temporal changes in clinical risk factors (e.g., older maternal age and complications of pregnancy) for these subtypes of preterm birth underlie the vagaries of the socioeconomic position–preterm birth relationship
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