(17-OH-)Progesterone is a precursor of cortisol and other steroid hormones, which is produced in the adrenal glands and to a lesser extent in the sex organs. It plays a role in hormone production but is not itself a classic "pregnancy hormone" like progesterone.
The value is primarily measured to detect disorders of adrenal function. Elevated values can occur in congenital adrenal hyperplasia, while low values are rarely significant.