Paediatric penile length: a systematic review and meta-analysis

To assess geographical variation in stretched penile length among prepubertal boys and evaluate temporal trends over the past two decades, as defining reference values for genital organ size remains crucial for early identification of development disorders.

The PubMed, Cochrane and Scopus databases (no deadlines for publishing were imposed) were searched according to the Preferred Reporting Items for Systematic Review and Meta-analyses statement. Five authors independently extracted individual participant data and assessed the risk of bias. Studies with quantitative penile lengths were included; those involving congenital malformations were excluded. The review protocol was prospectively registered in the International Prospective Register of Systematic Reviews (registration number CRD42022335643).

A total of 55 studies from 2000 to 2024 were evaluated, including data from 31 915 boys. Pooled mean stretched penile length estimates were 3.07 cm (95% confidence interval [CI] 2.88-3.26 cm) for the 1-week-old boys, 3.73 cm (95% CI 3.53-3.93 cm) for the 1-year-old boys, 4.69 cm (95% CI 4.49-4.88 cm) for the 2-5 year-old boys, and 5.43 cm (95% CI 5.20-5.66 cm) for the 5-10 year- old boys. When comparing data from the 2000s to the 2020s, stretched penile length decreased by 16.2% (from 3.46 to 2.90 cm), 16.3% (from 4.17 to 3.49 cm), 21.5% (from 5.31 to 4.17) and 26.2% (from 6.46 to 4.77 cm) in the 1-week-old, 1-year-old, 2-5-year-old and 5-10-year-old boys, respectively. Subgroup analysis for those aged >2 years showed significant variations by geographical region (P < 0.001).

The present study observed large variations in penile length across geographical regions and among prepubescent boys of different ages, while also suggesting a possible decline over the past two decades.