Effect of progesterone, administered via intravaginal rings, on serum concentrations of oestradiol, FSH, LH and prolactin in women

Abstract

Intravaginal rings containing progesterone were inserted on day 5 of the cycle to 8 healthy, normally menstruating women. Blood samples were taken during days 4-22 of the cycle at 2-3 day intervals. The plasma progesterone levels obtained after the insertion were between 7.5 and 21 nmol/l. Four subjects showed no increase in plasma estradiol concentrations. The subjects showing increased plasma estradiol levels also showed a positive feedback on LH [luteinizing hormone], resulting in ovulation or an LH peak. Progesterone may have a local inhibitory effect on the follicular estradiol production.