17α-hydroxyprogesterone (17-α-hydoxy progesterone, 17α-OHP) is a C-21 endogenous progesterone produced during the synthesis of glucocorticoids and sex steroids. Converted by progesterone, or by 17α-hydroxypregnenolone under the action of 3β-hydroxysteroid dehydrogenase, produced by adrenal cortex and gonad, its progesterone activity is very low. 17α-OHP is 21-hydroxylated to form the precursor compound S of cortisol. 17α-OHP in serum mainly works with sex hormones to promote the development of individual organs. 17α-OHP has circadian changes consistent with adrenal cortisol. The concentration of 17α-OHP in adult reproductive-age women varies with the menstrual cycle, and the luteal phase is higher than the follicular phase. During pregnancy, the fetus, placenta and adrenal glands can produce a large amount of 17α-OHP. 17α-OHP concentrations increase dramatically after 32 weeks of gestation until delivery, and 17α-OHP is also present in the umbilical cord blood of neonates. Clinically commonly used radioimmunoassay (RIA) to determine the level of 17α-OHP.