Associations between month/season of birth and health outcomes: an umbrella review of systematic reviews and meta-analyses

The relationship between month or season of birth and long-term health outcomes remains an important but underexplored topic in public health. Evidence suggests that birth timing may influence disease susceptibility and broader health trajectories, reflecting interactions between biological and ecological factors. Clarifying these associations is essential for advancing prevention and a holistic view of health shaped by temporal exposures.

We conducted an umbrella review of systematic reviews and meta-analyses indexed in PubMed, Embase, and Web of Science up to 2 July 2025. Eligible studies reported quantitative estimates for associations between birth month/season and objectively measured health outcomes. We used random-effects models to produce pooled estimates and evaluated heterogeneity, small-study effects, and bias. We graded associations using established class-of-evidence criteria and assessed methodological quality with AMSTAR 2.