Grant: IPPH Travel Awards - CPHA Annual Conference

Background Studies have shown improved birth outcomes for women of low socioeconomic position (SEP) receiving antenatal midwifery versus physician care. To understand for whom and under what circumstances this applies, we examined whether substance use, mental illness, social assistance, residence in a neighbourhood of low/moderate SEP, and teen maternal age modified the association between model of care (midwifery vs. physician) and small-for-gestational-age (SGA) or preterm birth (PTB) for women of low SEP. Methods For this retrospective cohort study, maternity data from the British Columbia (BC) Perinatal Data Registry were linked with Medical Services Plan (MSP) billing data. We report adjusted odds ratios (aORs) and 95% confidence intervals for SGA birth (< the 10th percentile) and PTB (< 37 weeks' completed gestation). For tests of interaction between antenatal models of care and psychosocial risk factors, p-values < 0.10 were considered statistically significant. Women were eligible for inclusion if they were residents of BC, carried a singleton fetus, had low to moderate medical/obstetric risk, birthed between April 1, 2008 and Dec. 31, 2012, and received an MSP subsidy (n=33,937). Results Midwifery vs. obstetrician patients had lower odds of PTB (aOR 0.53, 95% CI: 0.43-0.64). The difference was 31% lower among substance users (aOR 0.24, 95% CI: 0.11-0.54) compared to non-substance users (aOR 0.55, 95% CI: 0.44-0.68). For midwifery vs. obstetrician patients with both mental illness and substance use, odds of PTB were 34% lower (aOR 0.18, 95% CI: 0.06-0.55) compared to women with neither mental illness nor substance use (aOR 0.52, 95% CI: 0.41-.66). Effects were not statistically significantly different for midwifery vs. general practitioner patients with additional psychosocial risk. Conclusion Future studies should examine how antenatal models diverge in practice and if this systematically contributes to variation in birth outcomes.