Digit ratio (2D:4D) and prenatal/perinatal sex hormones: A response to Manning and Fink (2017)

I published a Letter to the Editor of Early Human Development [1] to provide an overview and discussion of the literature examining digit ratio (2D:4D) in relation to sex hormone concentrations measured from amniotic fluid and umbilical cord blood in humans. My reason was that there exist a vast number of papers reporting on 2D:4D as a proxy for prenatal sex hormone exposure, yet relatively few that have established associations with hormones assayed during the prenatal/perinatal periods of development. My conclusion was that although the literature points towards a negative correlation between 2D:4D and prenatal/perinatal androgen exposure, the link remains tenuous, with most reported effects not being statistically significant. Manning and Fink [2] responded to this Letter with three main points: (1) that there are currently six (rather than four) papers relating to 2D:4D and sex hormones measured from umbilical cord blood, (2) that statistically significant correlations between 2D:4D and perinatal androgen levels in males have been reported, and (3) that examination of maternal circulating sex hormones during the first trimester may present an opportunity to better understand how early exposure to sex hormones relates to 2D:4D in humans. I would like to take the opportunity to extend my thanks to Manning and Fink for raising these important points, and to Early Human Development for inviting me to write this response