Hi AKatie D
Yes there have been insufficient studies into the dosage of progesterone needed to protect the womb - these have mostly been done for low to medium doses of oestrogen and not very high oestrogen doses nor very low ones.
Yes we all respond differently but many HRT products are combined oestrogen and progesterone so the dose has to be worked out that does the job on average.
With separate products for oestrogen and progesterone it is possdible to tweak the dose but only underspecialist help or within licensing guidelines.
So - taking Utrogestan - two regimes are given: 2 x 100 mg for 12 days per 28 day cycle or daily 100 mg for continupis regimes. This may well be too much for very low oestrogen doses and too little for higher doses.
Some work has been done regarding alternate day dosing for vaginal utrogestan (some small studies) showing that half the oral dose can be used if taken vaginally to protect the womb, when taking low to medium dosdes of oestrogen As far as I recall the studies not not include high oestrogen doses.
It is not possible to compare one type of progesterone with another becauase their mode of delovery is different - it is the amount that gets to the womb to protect it that is important . If 45 mg Crinone is sufficient to protect the womb in the same way as 100 mg eg daily use, then it may well be that an equivalent amount is absorbed systemically even though the total dose sounds and is less - if you see what I mean. There will be studies looking into how much is absorbed into the body but I don't have them to hand. There is a thread I bumped recently which looked into some of this - you should be able to tell by the title - something like: vaginal utrogestan some studies...
It's certainly not possible to test how much progesterone you need from testing - because that's not how it works. When we take it as part of HRT we are artificially providing what the ovaries no longer produce or perhaps in insufficient amounts. Protection of the endometrium (womb lining) is the prime purpose of taking progesterone as part of hRT and the doses have been worked out through trials. It is not desirable to work this out by trial and error for every woman - but dosages can be tweaked under medical supervision. If you have a menopause clinic near you perhaps you can ask for a referral from your GP?
I sympathise with your feelings regarding lack of choice - this is echoed by many of us.
Is there anything we can help you with eg with menopausal symptoms or hRT?
Hurdity x