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.

食指与食指之间的长度之比（2D：4D）通常用作产前性激素暴露的指标。已经使用了几种方法来验证该方法，包括检查先天性肾上腺皮质增生（CAH）患者的2D：4D，这是一类特征为继发于类固醇生成不良的肾上腺雄激素产生的疾病。我们提出了系统的审查和荟萃分析，以检查这两个变量之间的关系。确定了与9个CAH队列相关的12篇文章，并且在其中8个队列的病例和对照之间进行了2D：4D比较。总共比较了n = 251位患有CAH的女性和n = 358位未受影响的女性，以及n = 108位CAH的男性和n = 204位未受影响的男性之间的至少一个2D：4D变量。先前的一项荟萃​​分析（Hönekopp和Watson，2010年）报告说，相对于性别匹配的对照，CAH患者的右手手指（R2D：4D）和左手手指（L2D：4D）的数字比率较低。我们的荟萃分析显示了相同的模式，R2D：4D的影响大小为中等，L2D：4D的影响大小较小。对于M2D：4D，也观察到较小的差异，对于D，未观察到明显的影响_[RL]。值得注意的是，按性别分层时，唯一具有统计学意义的效应是男性的R2D：4D和女性的L2D：4D，自Hönekopp和Watson（2010）的荟萃分析以来，平均效应大小降低了46.70％。我们还发现，该文献中的个人比较功能不足，并且在CAH样本中2D：4D的性二态性模式与典型的发展中人群相似。讨论了有关产前雄激素假说的发现以及其他解释。