Risk factors of under-five and infant mortality: An umbrella review of systematic reviews and meta-analyses.

Background: Ensuring child survival is a critical global challenge, requiring a robust and comprehensive understanding of the risk factors contributing to under-five mortality (U5M). We aimed to synthesise and summarise the current available evidence on risk factors of U5M and infant mortality worldwide to inform global child health programmes. Methods: We searched six major databases (Embase, Medline, Scopus, CINAHL, Web of Science, and Global Health) and repositories of systematic reviews, as well as grey literature sources to identify systematic reviews and meta-analyses that examined the associations between risk factors of U5M and infant mortality between 1 January 1990 and 4 March 2024. The quality of reviews was assessed using A Measurement Tool to Assess Systematic Reviews, Version 2 (AMSTAR 2). The strength of evidence and direction of associations was graded. Results: Of 5684 records, we included 32 reviews (including five systematic reviews without meta-analysis) which comprised 1042 primary studies. We synthesised 28 and 29 unique risk factors associated with U5M and infant mortality, respectively. Although there was no convincing evidence for the risk factors, we found probable evidence of association between exclusive breastfeeding (consistent negative association), and maternal death (consistent positive association) with U5M. There was also probable evidence for the association of short (<18 months) interpregnancy intervals (less consistent negative association), pre-pregnancy maternal obesity (consistent positive association), and maternal HIV infection (consistent positive association) with infant mortality. Conclusions: While the review identified a broad range of risk factors, the overall evidence for most factors associated with under-five and infant mortality was 'limited-suggestive' or 'limited and no conclusive'. Thus, further high-quality studies are required to strengthen the evidence on these risk factors. Registration: PROSPERO CRD42023455542.