The Relationship Between Finger Ratio and Development in Infants

One of the most prominent indicators of prenatal androgen exposure is considered to be the ratio of second and fourth finger lengths (2D:4D). The 2D:4D finger ratio refers to the ratio of the length of the second finger (2D; index finger) and the fourth finger (4D; ring finger). Evidence suggests that 2D:4D is developmentally stable and stabilizes from the second trimester of pregnancy. It has been reported that the 2D:4D ratio correlates positively with estrogen and negatively with testosterone. In both sexes, prenatal testosterone levels are inversely related by a 2D:4D ratio, which does not change with age. Androgens can have direct trophic effects on target cells or indirectly affect neuronal growth through neurotrophic mediators released locally by steroid-sensitive neuronal or glial cells. Prenatal testosterone can have long-term organizational effects on the structure and function of various body systems (e.g., cardiovascular and musculoskeletal systems) that are important for physical activity and exercise.