If suspected, a test can be done to detect the presence of the male Y-chromosomes in some circulating white blood cells of the subject. Genetic testing for the Y-chromosome can be performed within days of birth and can aid in the early identification of a sterile female bovine.

Physical examination of the calf may also reveal differences: frequently freemartin heifers have at the ventral tip of their vulva a tuft of hair which is distinctive in these individuals, which is a subjective assessment. Also, many (but not all), freemartins have a shortened vagina compared with that of a fertile heifer.

A freemartin is the normal outcome of mixed twins in all cattle species which have been studied. It does not normally occur in most other mammals, though it has been recorded in sheep, goats, pigs, deer, and camels.