Withdrawal bleeding with progesterone seen in otherwise amenorrheic woman due to:

If a patient is having positive progesterone challenge i.e. bleeding occurs after giving progesterone it means: If withdrawal bleeding occurs, it proves— (i) The intact hypothalamopituitary ovarian axis and (ii) There is adequate endogenous estrogens (serum E2 level more than 40 pg/ml) to promote progesterone receptors in the endometrium, (iii) Anatomically patent outflow tract and (iv) Endometrium is responsive. The defect lies in production of progesterone (as when progesterone is supplemented from outside, it results in withdrawal bleeding) and since progesterone is produced mainly by corpus luteum, so, the defect is anovulation. The main cause of Anovulation in a case of 2° amenorrhea is polycystic ovarian disease.