Effect of season of birth on cord blood IgE and IgE at birth: A systematic review and meta-analysis

- Findings are inconsistent on which season of birth is associated with risk of high cord blood.
- Due to varying cut-off values for IgE and exposure definitions, a crude multivariate meta-analysis was used.
- Winter birth was associated with a weak increase in risk of elevated IgE.

BackgroundElevated cord blood IgE is important on the pathway to allergic disease. The association between season of birth and infant cord blood IgE is not well-established. Study findings differ on which birth season is associated with higher cord blood IgE risk and its magnitude. We conducted a systematic review and meta-analysis of studies on season of birth and cord blood IgE.MethodsWe searched Medline, Web of Science, Scopus and ProQuest Health databases, and reviewed reference lists of articles that met the inclusion criteria. All included studies measured IgE as a binary variable using various cut-off values. We performed multivariate-random-effects meta-analysis to handle an exposure with multiple categories of Season of Birth.ResultsOur search identified 275 records and 10 had sufficient data to be included in a meta-analysis. Relative to summer, winter birth had the greatest odds of high IgE (≥ 0.1 IU/ml), meta-analysis OR = 1.24 (95%CI: 1.01-1.52). A similar OR, was found for IgE ≥ 0.5 IU/ml, OR = 1.30 (95%CI: 0.99-1.71).ConclusionsA winter season of birth was associated with statistically significant higher odds of elevated cord blood IgE at cut-off ≥ 0.1 IU/ml but borderline at cut-off ≥ 0.5 IU/ml. This winter effect is likely to be a marker for a range of other environmental exposures during specific stages of pregnancy, such as aeroallergen exposures, maternal infections and vitamin D levels. Further research is required to support our finding and to identify the exact mechanisms that lead to the winter season of birth effect on circulating IgE levels, as this may have implications for allergic disease prevention.