czattau - I understand your frustration, and I think it is a valid point. I may be naive, but I am not worried about progesterone levels with the ring... here's why:
if you search "progesterone ring ivf", the first hit you will see is a paper on essentially the same study done in chile, columbia and brazil with 505 people, except they compared the ring to im progesterone injections. They cover previous studies comparing im progesterone and gel, and they are similar in effectiveness.
The paper discusses progesterone levels measured by blood tests from those with the ring and those with im progesterone injections, and I think the reason why they do not want to measure blood levels is in there. Vaginal administration affects the uterine lining just as much as im progesterone, but im travels through the blood, and the vaginal delivery system does so at a lesser degree. The vaginal delivery has a more direct route to the uterus, so progesterone blood levels might not be the best way to measure its effect.
Overall, the clinical pregnancy rate was the same in both groups. Implantation rate was almost identical (15.9 vs 16%). There were some significant differences in women with premature ovarian failure, where the ring was more effective.
Also, this ring has been used in nursing women as a form of contraceptive. If effectiveness was questionable, or side effects were horrible, it would not have been used for years so far.
So I think that the gel is more of a known factor in the US, but the ring is also very much tested. This study is only one, and there have been many others since then, several of which were in the US.
IndieBlue - I have not tried the muscle contraction technique

I don't want to take it in and out again until I have to on Mon or Wed, but I'll try it then and let you know how it goes. I had more trouble getting it up there far enough than getting it out.
Today I have no discomfort, so I guess I was just sore from the retrieval and it wasn't the ring.
Also, Beccatx- I don't think supplementation with higher progesterone levels could stop a miscarriage. I've been unfortunate enough to have two, and from what I've read and the doctors I've talked to, it would not stop the progression. I agree that having a normal level is essential, especially during IVF when we can't make progesterone ourselves, but that might be the reason for the assistant's vague answer?
Indieblue - I would be careful about herbals. You cannot control your dosage with that cream, and herbals are not regulated with regard to dosage, and uniformity. My center told me not to use herbals at all during the study.