Socioeconomic gradients of adverse birth outcomes and related maternal factors in rural and urban Alberta, Canada: a concentration index approach

OBJECTIVE: Using a summary measure of health inequalities, this study evaluated the distribution of adverse birth outcomes (ABO) and related maternal risk factors across area-level socioeconomic status (SES) gradients in urban and rural Alberta, Canada. DESIGN: Cross-sectional study using a validated perinatal clinical registry and an area-level SES. SETTING: The study was conducted in Alberta, Canada. Data about ABO and related maternal risk factors were obtained from the Alberta Perinatal Health Program between 2006 and 2012. An area-level SES index derived from census data (2006) was linked to the postal code at delivery. PARTICIPANTS: Women (n=3 30 957) having singleton live births with gestational age ≥22 weeks. PRIMARY AND SECONDARY OUTCOME MEASURES: We estimated concentration indexes to assess inequalities across SES gradients in both rural and urban areas (CIdx(R) and CIdx(U), respectively) for spontaneous preterm birth (PTB), small for gestational age (SGA), large for gestational age (LGA), gestational hypertension, gestational diabetes, smoking and substance use during pregnancy and pre-pregnancy weight >91 kg. RESULTS: The highest health inequalities disfavouring low SES groups were identified for substance abuse and smoking in rural areas (CIdx(R)−0.38 and −0.23, respectively). Medium inequalities were identified for LGA (CIdx(R)−0.08), pre-pregnancy weight >91 kg (CIdx(R)−0.07), substance use (CIdx(U)−0.15), smoking (CIdx(U)−0.14), gestational diabetes (CIdx(U)−0.10) and SGA (CIdx(U)−0.07). Low inequalities were identified for PTB (CIdx(R)−0.05; CIdx(U)−0.05) and gestational diabetes (CIdx(R)−0.04). Inequalities disfavouring high SES groups were identified for gestational hypertension (CIdx(R)+0.04), SGA (CIdx(R)+0.03) and LGA (CIdx(U)+0.03). CONCLUSIONS: ABO and related maternal risk factors were unequally distributed across the socioeconomic gradient in urban–rural settings, with the greatest concentrations in lower SES groups of rural areas. Future research is needed on underlying mechanisms driving SES gradients in perinatal health across the rural–urban spectrum.