Low digit ratio (2D:4D) is associated with delayed menarche.

The prenatal environment of the human fetus is now known to have lasting physiological and behavioral effects into childhood and adulthood. The objective of this study was to examine the relationship between early testosterone exposure, as measured by the ratio of the length of the 2nd and 4th digits (2D:4D ratio), and age of menarche. Retrospective, self-report data on menarcheal age were obtained from 206 healthy female college students, as well as finger length ratio data from both hands. Low right-hand 2D:4D ratios (but not left-hand) were associated with delayed menarche. The results provide evidence for an androgen-delayed menarche link and suggest that this relationship can be continuous in nature and not always categorical as occurs in congenital adrenal hyperplasia, hyperandrogenism, or polycystic ovary syndrome. Copyright 2008 Wiley-Liss, Inc.