Carrie...this is the only one I could find from memory...I can't remember what search terms I used...arrgh

Quote:
The recent development of a new sustained release vaginal progesterone gel, Crinone 4%, showed that using less progesterone (because of the sustained release effects) nonetheless achieved endometrial results similar to findings made with IM progesterone administration or in the menstrual cycle. This led to the unexpected discovery of uterine trophicity of vaginal progesterone. In a prospective trial, Fanchin et al. (4) demonstrated that every other day administration of 1.1 g of Crinone 4% gel containing 45 mg of progesterone induced full endometrial decidualization, despite progesterone levels in peripheral blood that were in the "luteal phase defect" range (peaks at < 5 ng/mL and troughs at ≤ 1 ng/mL).

The discrepancy between low peripheral levels of progesterone and full effects on the nedometrium led us to postulate that some of the progesterone administered vaginally is directly transported into the uterus through a "first uterine pass effect" (5). In a recent study (6), we showed that vaginal progesterone administration resulted in higher uterine tissue concentrations of progesterone and lower peripheral blood levels as compared to IM progesterone administration. These results also refuted the objections raised by Miles data hypothesizing that the study findings might reflect a contamination of the biopsy specimens by progesterone still present in the vagina. the vaginal gel Crinone confirmed the prior work of Miles et al (7) that used locally made vaginal progesterone capsules. The results also refuted the objection raised to the Miles data that higher uterine tissue concentrations following vaginal progesterone administration resulted from contamination of the uterine aspirate by progesterone still present in the vagina. In Cicinelli’s study, endometrial tissue was obtained from hysterectomy specimens which, thus, ruled out any possible contamination.

Some doctors also don't like to give women at risk of OHSS the injections because they progesterone is in such a high concentration that it can affect the ovaries adversely. I guess it is another case of horses for courses in this wonderful world of assisted conception.