About hydroxyprogesteronea c-21 steroid hormone,progestagen, progestational agent, diagnostic aid( estrogen production).mechanism of action of hydroxyprogesteroneit is a progestin derivative exerts it`s action through nuclear progesterone receptors situated in female genital tract, breast, cns, and pituitary. when the drug binds to progesterone receptors it undergoes dimerization and attaches to progesterone response element of target genes and regulates transcription through coactivators- which ultimately leads to modification of protein synthesis. it contributes to proper development and maintenance of female sexual functions. it prepare uterus for nidation and maintenance of pregnancy. it prevents endometrial shedding, decreases uterine motility, and also inhibits immunological rejection of the foetus by decreasing t-cell function and cell mediated immunity.