Hand with index finger being shorter than the ring finger, resulting in a small 2D:4D ratio, pointing to a high exposure to testosterone in the uterus.

Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior

...

A third focus for future research might be on identifying additional ways to assess the early hormone environment in healthy individuals. The literally hundreds of studies that have been published in the past dozen or so years relating the 2D:4D finger ratio to various behaviors and other characteristics that show sex differences provide evidence of interest in such measures. Unfortunately, studies of 2D:4D have produced inconsistent results, even in large samples. Another approach has been to look at testosterone in amniotic fluid samples, but this approach is limited to women referred for amniocentesis for clinical reasons, so not necessarily representative of the general population. In addition, only one sample of amniotic fluid at a single timepoint, usually uncontrolled for time of day, is available. One report on extreme groups from a large population sample suggests that maternal testosterone during pregnancy might provide a window into the hormone environment of the female fetus [72]. Although maternal hormones appear far from fetal hormones, there appears to be a substantial correlation between the two [46], probably because of genetic relatedness [60;128]. One advantage of maternal samples, either of blood or of saliva, is that they can be obtained repeatedly in the population at large. This potential window into hormones during early development deserves additional attention.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3296090/