Prevalence of diabetes in pregnancy among Indigenous women in Australia, Canada, New Zealand, and the USA: a systematic review and meta-analysis

Background: Indigenous peoples in countries with similar colonial histories have disproportionate burdens of disease compared with non-Indigenous peoples. We aimed to systematically identify and collate studies describing the prevalence of pre-existing diabetes and gestational diabetes, and compare the prevalence of these conditions between Indigenous and non-Indigenous pregnant women in Australia, Canada, New Zealand, and the USA. Methods: For this systematic review and meta-analysis, an information specialist did a comprehensive search of eight databases (Ovid MEDLINE, Ovid Embase, Ovid Global Health, CINAHL [EBSCO], Scopus, ProQuest Dissertations and Theses Global, PROSPERO, and the Wiley Cochrane Library) in June, 2019, for studies published between inception and June 25, 2019, without restrictions on language, publication type, or year of publication. Database searches were supplemented by grey literature searches of the Bielefield Academic Search Engine and Google Scholar, and the reference lists of relevant articles were also manually searched. We included observational epidemiological studies comparing the prevalence of pre-existing diabetes or gestational diabetes in Indigenous and non-Indigenous pregnant women in Australia, Canada, New Zealand, and the USA. Two independent reviewers assessed study eligibility and risk of bias. We used a standardised data extraction form to collect information from the published reports of eligible studies, and, if needed, we contacted authors for further information. We did a Mantel-Haenszel random-effects meta-analysis to obtain the pooled unadjusted prevalence odds ratios (PORs) of pre-existing diabetes and gestational diabetes in Indigenous women compared with non-Indigenous women. We stratified meta-analyses by country and type of diabetes. The study is registered with PROSPERO, number CRD42018095971. Findings: Our search identified 1348 studies, of which 43 studies with 32 952 441 participants from Australia, Canada, New Zealand, and the USA were included in the systematic review, and 39 of these studies were included in the meta-analysis. 40 of the included studies used a cohort design. Pre-existing diabetes was more prevalent in Indigenous women than in non-Indigenous women, with pooled PORs ranging from 1·81 (95% CI 1·53–2·13) for women in the USA to 3·63 (2·35–5·62) for women in Australia. Similarly, gestational diabetes was more prevalent in Indigenous women than in non-Indigenous women, with PORs ranging from 1·42 (1·24–1·63) for women in Australia to 2·04 (1·46–2·84) for women in Canada. Risk of bias was low in 37·2% of studies, unclear in 34·8% of studies, and high in 27·9% of studies. Heterogeneity between studies was predominantly high (I2=97–100%), with one exception of moderate heterogeneity (I2=48%); however, the magnitude and direction of the PORs from individual studies indicated an association between pre-existing diabetes or gestational diabetes and indigeneity among pregnant women. Interpretation: The prevalence of pre-existing diabetes and gestational diabetes was higher in Indigenous pregnant women than in non-Indigenous pregnant women in four countries (Australia, Canada, New Zealand and the USA) with similar histories of colonialism. These findings have implications for prenatal care services and the monitoring of Indigenous women in industrialised countries. Funding: Canadian Institute of Health Research and the Women's and Children's Health Research Institute.