implying low androgen exposure during fetal life) ( Klimek et al., 2014 Oh et al., 2014). Several cross-sectional studies have reported low sperm counts, decreased testicular volume and impaired hormonal status in adult men having higher digit ratios (i.e. Since the 2D:4D is sexually dimorphic at birth, and under the hypothesis that this difference is related to in utero androgens levels, several studies have evaluated the association between 2D:4D as a marker of prenatal androgen exposure and different reproductive outcomes across the life course. The direction and magnitude of these associations as illustrated below, however, have not been consistent. Associations between digit ratios and several health outcomes including male fertility, sexual orientation, physical performance, hand preference and autism have been reported ( Breedlove, 2010). As such, lower 2D:4Ds could be potential indicators of greater androgen exposure during fetal development ( Manning et al., 1998). The 2D:4D is a sexually dimorphic trait, with males having relatively shorter 2nd than 4th digit lengths ( Manning et al., 1998). The 2D:4D ratio reflects sexual differentiation early in life and may be an end-point for the organizational effects of prenatal androgens in the human body. A novel end-point in humans that has been proposed as an indicator of sexual development is the 2nd (index) to 4th (ring) finger digit ratio (2D:4D). There is a paucity of endocrine-sensitive end-points that allow the epidemiological assessment of diverse life-course stressors on developmental and reproductive functions ( Arbuckle et al., 2008). Developmental origins of health and disease, digit ratios, time to pregnancy, fecundity, prenatal androgen exposure Introduction
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