What is the evidence for a link between digit ratio (2D:4D) and direct measures of prenatal sex hormones?

06 Oct 2017

Since Manning et al.'s seminal paper was published in 1998, the ratio of length between the second (index) and fourth (ring) fingers (digit ratio, or 2D:4D) has been commonly employed by researchers as an indicator of prenatal sex hormone exposure. However, although an extensive literature now exists on how 2D:4D relates to a range of phenotypic outcomes, to the best of my knowledge there are currently only six papers that examine 2D:4D in relation to direct measures of prenatal sex hormones. Furthermore, the hormones reported on in four of these papers were measured from umbilical cord blood sampled shortly after birth. Although the blood might relate to foetal circulation in late gestation, the hormone levels measured technically relate to the perinatal rather than prenatal period (for a comparison of methods for measuring foetal sex hormones, see van de Beek et al.).