Unraveling the link between birth order and blood pressure: insights from a comprehensive systematic review and meta-analysis

The objective of the present systematic review was to incorporate previous studies investigating the association of birth order with the risk of systolic and diastolic blood pressure (DBP). We employed random-effects and Bayesian meta-analyses, complemented by subgroup and sensitivity analyses, including funnel plots, Begg's rank correlation test, Egger's linear regression test, Galbraith plots, and leave-one-out meta-analysis. Of the 13 articles analyzed, 92% (12 articles) were published from 2010 onwards. The aggregate sample comprised 466 853 firstborns and 646 786 later-born individuals. Geographically, the studies were primarily conducted in Europe (54%), followed by Asia (23%), and America (23%). The pooled mean difference for systolic blood pressure (SBP) under a random-effects model was 0.28 mm Hg (95% CI: −7.03 to 7.59), and for DBP was 0.33 mm Hg (95% CI: −5.38 to 6.04), neither of which reached statistical significance (SBP: Z = 0.08, P = 0.939; DBP: Z = 0.11, P = 0.910). Sensitivity analyses supported these findings. Bayesian meta-analysis presented a 95% credible interval for SBP and DBP ranging from −7.25 to 7.84 and −5.60 to 6.27, respectively. The investigation found no substantial evidence of a significant difference in SBP and DBP between firstborns and later-born individuals, challenging the hypothesis that birth order significantly impacts blood pressure levels. ID registration number: 567971.