Diagnosis of Pinworm Infestation Examination of the perianal region for worms, ova, or both Pinworm infestation can be diagnosed by finding the female worm, which is 8 to 13 mm long (males are 2 to 5 mm), in the perianal region 1 or 2 hours after a child goes to bed at night or in the morning or by using a low-power microscope to identify ova on cellophane tape.