Early mortality among aboriginal and non-aboriginal women who had a preterm birth in Western Australia: A population-based cohort study.

Abstract

Having a preterm (<37 weeks' gestation) birth may increase a woman's risk of early mortality. Aboriginal and Torres Strait Islander (hereafter Aboriginal) women have higher preterm birth and mortality rates compared with other Australian women. We investigated whether a history of having a preterm birth was associated with early mortality in women and whether these associations differed by Aboriginal status. This retrospective cohort study used population-based perinatal records of women who had a singleton birth between 1980 and 2015 in Western Australia linked to Death Registry data until June 2018. The primary and secondary outcomes were all-cause and cause-specific mortality respectively. After stratification by Aboriginal status, rate differences were calculated, and Cox proportional hazard regression was used to estimate adjusted hazard ratios (HR) and 95% confidence intervals (CI) for all-cause and cause-specific mortality. There were 20,244 Aboriginal mothers (1349 deaths) and 457,357 non-Aboriginal mothers (7646 deaths) with 8.6 million person-years of follow-up. The all-cause mortality rates for Aboriginal mothers who had preterm births and term births were 529.5 and 344.0 (rate difference 185.5, 95% CI 135.5, 238.5) per 100,000 person-years respectively. Among non-Aboriginal mothers, the corresponding figures were 125.5 and 88.6 (rate difference 37.0, 95% CI 29.4, 44.9) per 100,000 person-years. The HR for all-cause mortality for Aboriginal and non-Aboriginal mothers associated with preterm birth were 1.48 (95% CI 1.32, 1.66) and 1.35 (95% CI 1.26, 1.44), respectively, compared with term birth. Compared with mothers who had term births, mothers of preterm births had higher relative risks of mortality from diabetes, cardiovascular, digestive and external causes. Both Aboriginal and non-Aboriginal women who had a preterm birth had a moderately increased risk of mortality up to 38 years after the birth, reinforcing the importance of primary prevention and ongoing screening.