Digit ratio (2D:4D) and congenital adrenal hyperplasia (CAH): Systematic literature review and meta-analysis

Gareth Richards*, Wendy Browne, Ezra Aydin, Mihaela Constantinescu, Gideon Nave, Mimi Kim, Steven James Watson

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

15 Citations (Scopus)
41 Downloads (Pure)


The ratio of length between the second and fourth fingers (2D:4D) is commonly used as an indicator of prenatal sex hormone exposure. Several approaches have been used to try to validate the measure, including examining 2D:4D in people with congenital adrenal hyperplasia (CAH), a suite of conditions characterised by elevated adrenal androgen production secondary to defective steroidogenesis. We present a systematic review and meta-analysis that examines the relationship between these two variables. Twelve articles relating to nine CAH cohorts were identified, and 2D:4D comparisons have been made between cases and controls in eight of these cohorts. Altogether, at least one 2D:4D variable has been compared between n = 251 females with CAH and n = 358 unaffected females, and between n = 108 males with CAH and n = 204 unaffected males. A previous meta-analysis (Hönekopp and Watson, 2010) reported lower right hand (R2D:4D) and left hand (L2D:4D) digit ratios in patients with CAH relative to sex-matched controls. Our meta-analysis showed the same pattern, with medium effect sizes for R2D:4D and small effect sizes for L2D:4D. Differences of small magnitude were also observed for M2D:4D, and no significant effects were observed for D[R-L]. Notably, the only effects that remained statistically significant when stratified by sex were R2D:4D in males and L2D:4D in females, and the average effect size had reduced by 46.70% since the meta-analysis of Hönekopp and Watson (2010). We also found that individual comparisons in this literature were considerably underpowered, and that patterns of sexual dimorphism in 2D:4D were similar in CAH samples as in typically developing populations. Findings are discussed in relation to the prenatal androgen hypothesis as well as alternative explanations.
Original languageEnglish
Article number104867
JournalHormones and Behavior
Early online date6 Oct 2020
Publication statusPublished - 1 Nov 2020


  • 2D:4D
  • Congenital adrenal hyperplasia
  • Digit ratio
  • Foetal testosterone
  • Meta-analysis
  • Prenatal sex hormones


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