However, it should be noted that this effect size estimate for D may be attenuated this is due to it having been derived from self-measured finger lengths, which are known to be associated with high levels of random measurement error 8. Small-to-medium sized sex differences (male < female) are reliably observed for R2D:4D ( d = 0.457) and L2D:4D ( d = 0.376) 9, but that for D appears to be much smaller ( d = 0.065) 8. Low R2D:4D relative to L2D:4D has been suggested to reflect high prenatal androgen exposure 6– 8.

Researchers typically measure digit ratios for the right hand (R2D:4D) and/or left hand (L2D:4D), though sometimes also examine directional asymmetry (D ). More specifically, it has been suggested that a high concentration of testosterone 1, 2 or high ratio of testosterone-to-estradiol (T:E) 3– 5 during prenatal development results in low 2D:4D. The ratio of second (index) to fourth (ring) finger length (digit ratio or 2D:4D) has been hypothesised to reflect individual differences in prenatal exposure to sex hormones. Taken together, the results of our study suggest research with larger samples is required to determine whether digit ratios are valid proxies for maternal sex hormone exposure. However, the first of these effects is in the opposite direction to that predicted by theory. Nevertheless, the multivariate level of analysis did reveal that T correlated positively with left hand digit ratio (L2D:4D) and negatively with D.

Although the testosterone (T) to estradiol (E) ratio correlated negatively with right hand digit ratio (R2D:4D) and directional asymmetry (right-minus-left) in digit ratio (D ), neither effect remained statistically significant once demographic and obstetric covariates were controlled for. We report the first pre-registered study to investigate mothers’ early pregnancy sex hormone concentrations in relation to their children’s digit ratios measured at 18–22-month follow-up. The ratio of index to ring finger (2D:4D) has been hypothesised to indicate prenatal androgen exposure, yet evidence for its validity is lacking.

2d 4d ratio testosterone