Digit ratio (2D:4D) and maternal testosterone-to-estradiol ratio measured in early pregnancy

Funder: NIHR Cambridge Biomedical Research Centre; doi: http://dx.doi.org/10.13039/501100018956
Funder: NIHR Brain Injury MedTech Co-operative
Funder: Autism Research Trust
Funder: Simons Foundation Autism Research Initiative; doi: http://dx.doi.org/10.13039/100014370
Funder: Templeton World Charitable Fund
Funder: Medical Research Council; doi: http://dx.doi.org/10.13039/501100000265
Funder: NIHR Collaboration for Leadership in Applied Health Research and Care East of England at Cambridgeshire and Peterborough NHS Foundation Trust
Funder: Innovative Medicines Initiative 2 Joint Undertaking under grant agreement No 777394 for the project AIMS-2-TRIALS
The ratio of index to ring finger (2D:4D) has been hypothesised to indicate prenatal androgen exposure, yet evidence for its validity is lacking. 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. 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[R−L]), neither effect remained statistically significant once demographic and obstetric covariates were controlled for. Nevertheless, the multivariate level of analysis did reveal that T correlated positively with left hand digit ratio (L2D:4D) and negatively with D[R−L]. However, the first of these effects is in the opposite direction to that predicted by theory. 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.