According to a study in Environmental Health Perspectives, the size of a man's "anogenital distance" (or, more colloquially, "taint") is a good predictor of fertility:
"It's non-invasive and anybody can do it, and it's not sensitive to the kinds of things that sperm count is sensitive to, like stress or whether you have a cold or whether it's hot out," Swan said in a telephone interview.
"If somebody's got a short AGD, particularly if they have problems conceiving, I would say get to the infertility doctor, because the chances are good that something is wrong."
To reach their conclusions, researchers measured the AGDs of 126 men born in or after 1988, a small but statistically significant sample, Swan said.
Key genital measurement linked to male fertility
(Image: Phallic Parsnip3311, a Creative Commons Attribution (2.0) image from fireflies604's photostream)