The ratio of two digits in particular – the palmar 2nd (index finger) and 4th (ring finger) – is affected by fetal exposure to hormones, in particular to testosterone, and other androgens; this 2D:4D ratio can be considered a crude measure for prenatal androgen exposure, with lower 2D:4D ratios pointing to higher prenatal androgen exposure. There are also studies that suggest that the palmar 2D:4D ratio is influenced by prenatal estrogen exposure, and that it thus correlates negatively not with prenatal testosterone alone, but rather with the prenatal testosterone-to-estrogen ratio (T:O).