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Open Access Research article

Effects of socioeconomic position and clinical risk factors on spontaneous and iatrogenic preterm birth

KS Joseph1*, John Fahey2, Ketan Shankardass3, Victoria M Allen4, Patricia O’Campo5, Linda Dodds6, Robert M Liston7 and Alexander C Allen6

Author Affiliations

1 Department of Obstetrics and Gynaecology and the School of Population and Public Health, University of British Columbia and the Children’s and Women’s Hospital of British Columbia, 4500 Oak Street, Vancouver, British Columbia V6H 3 N1, Canada

2 Reproductive Care Program of Nova Scotia, Halifax, Nova Scotia, Canada

3 Department of Psychology, Wilfred Laurier University, Waterloo, Ontario, Canada

4 Department of Obstetrics & Gynaecology, Dalhousie University and the IWK Health Centre, Halifax, Nova Scotia, Canada

5 Centre for Research on Inner City Health, St. Michael’s Hospital and the University of Toronto, Toronto, Ontario, Canada

6 Perinatal Epidemiology Research Unit, Departments of Obstetrics & Gynaecology and Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, Nova Scotia, Canada

7 Department of Obstetrics and Gynaecology, University of British Columbia, and the Children’s and Women’s Hospital of British Columbia, Vancouver, British Columbia, Canada

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BMC Pregnancy and Childbirth 2014, 14:117  doi:10.1186/1471-2393-14-117

Published: 27 March 2014

Abstract

Background

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.

Methods

We 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.

Results

The 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).

Conclusions

Socioeconomic 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.

Keywords:
Spontaneous preterm birth; Iatrogenic preterm birth; Risk factors; Pregnancy complications; Socioeconomic status