Low birth weight and maternal incarceration in pregnancy: A longitudinal linked data study of Western Australian infants

Rationale: Improved birth weight outcomes have been reported for infants of mothers imprisoned during pregnancy relative to similarly disadvantaged mothers, however, findings are equivocal and evidence is lacking from jurisdictions outside the United States. Objective: To investigate whether maternal imprisonment during pregnancy is a determinant of low birth weight (<2500 g) for Indigenous and non-Indigenous infants in Western Australia. Methods: A longitudinal sample of 41,910 singleton infants born in Western Australia (October 1985-December 2013), was identified with linked administrative data and examined by five mutually exclusive categories of maternal corrections history; (i) imprisonment in pregnancy, (ii) imprisonment before pregnancy, (iii) first imprisonment after birth, (iv) community-based corrections record without imprisonment at any time, and (v) no corrections record at any time. Univariate and multivariate Poisson regression was performed to determine key risk factors for low birth weight. Prevalence of risk factors were calculated by maternal corrections history. Results: After adjusting for other significant pregnancy risks, maternal imprisonment before (Indigenous RR 2.02, 95%CI 1.84–2.22, p<.001; non-Indigenous RR 2.48, 95%CI 1.98–3.12, p<.001) or during (Indigenous RR 1.96, 95%CI 1.68–2.29, p<.001; non-Indigenous RR 2.12, 95%CI 1.48–3.03, p<.001) pregnancy remained strong determinants of low birth weight, and carried greater risk than imprisonment after birth (Indigenous RR 1.58, 95%CI 1.44–1.74, p<.001; non-Indigenous RR 1.75, 95%CI 1.51–2.04, p<.001) or community-based corrections orders (Indigenous RR 1.32, 95%CI 1.21–1.43, p<.001; non-Indigenous RR 1.40, 95%CI 1.05–1.88, p<.001), relative to no corrections record. Pregnancy risk factors more prevalent amongst infants whose mothers were imprisoned before or during pregnancy included substance-use related service contacts, hospitalisation for injury, mental health service contacts, and having a sibling in contact with the child protection system. Conclusion: Western Australian infants with mothers imprisoned before or during pregnancy experience elevated risk of low birth weight and exposure to maternal substance use, injury and mental distress in pregnancy.