Neighbourhood Income and Risk of Having an Infant With Concomitant Preterm Birth and Severe Small for Gestational Age Birth Weight

Abstract

Objective: Socioeconomic position gradients have been individually demonstrated for preterm birth (PTB) at <37 weeks gestation and severe small for gestational age birth weight at <5th percentile (SGA). It is not known how neighbourhood income is related to the combination of PTB and severe SGA, a state reflective of greater placental dysfunction and higher risk of neonatal morbidity and mortality than PTB or severe SGA alone.

Methods: This population-based study comprised all 1 367 656 singleton live births in Ontario from 2002 to 2011. Multinomial logistic regression was used to estimate the odds of PTB with severe SGA, PTB without severe SGA, and severe SGA without PTB, compared with neither PTB nor severe SGA, in relation to neighbourhood income quintile (Q). The highest income quintile, Q5, served as the exposure referent. Adjusted odds ratios (aORs) were adjusted for maternal age at delivery, parity, marital status, and world region of birth (Canadian Task Force Classification II-2).

Results: Relative to women residing in Q5 (2.3 per 1000), the rate of PTB with severe SGA was highest among those in Q1 (3.6 per 1000), with an aOR of 1.34 (95% confidence interval [CI] 1.20-1.50). The corresponding aORs were 1.23 (95% CI 1.09-1.37) for Q2, 1.14 (95% CI 1.02-1.28) for Q3, and 1.06 (95% CI 0.95-1.20) for Q4. Less pronounced aORs were seen for each individual outcome of PTB and severe SGA.

Conclusion: Women residing in the lowest-income areas are at highest risk of having a fetus born too small and too soon. Future research should focus on identifying those women most predisposed to combined PTB and severe SGA.

Keywords: infant, small for gestational age; pregnancy outcomes; premature birth; socioeconomic factors.