Hi there Maryjane - just had a quick Google using these words:
insert vagifem lower third of vagina
and got this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3252029/This is the relevant extract:
"Vaginal Estrogen and the Endometrium
Intravaginal application of estrogen plays a unique role in hormone replacement therapy because of evidence that there is preferential delivery of hormones supplied in the vagina to the endometrium. This has been termed the “first uterine pass effect.†This phenomenon is theorized to be the result of countercurrent exchanges with vein to artery diffusion. While this phenomenon is known to occur in the upper third of the vagina; it was unclear if this occurs throughout the vagina. A recent study examined this phenomenon. Vagifem® was applied in postmenopausal women either in the lower or upper third of the vagina. Estradiol levels along with Doppler velocity measurements were made both at baseline and after 2 hours. Application to the upper third of the vagina resulted in statistically significant higher serum estradiol levels but only a small absolute difference compared to the lower third of the vagina. Also, with application of Vagifem® to the upper third of the vagina, there was a decrease in pulsatility index and resistance index which was not seen with lower third application. Thus, the first pass uterine effect appears to be exclusive to the upper third of the vagina. With application to the lower third of the vagina there was preferential delivery to the periurethral area. 47 "
The "recent study" which is summarised in the review is this one:
47. Cicinelli E, DeZiegler D, Morgese S, et al. “First uterine pass effect†is observed when estradiol is placed in the upper but not lower third of the vagina. Fertil Steril. 2004;81:1414–1416. [PubMed] [Google Scholar]
So the study was not looking at differences in efficacy that you mentioned but specifically the effect on the uterus.
There may be other studies that you are looking for?
Hope this helps
Hurdity x