pollie, yes it is strange. I can only give you my personal experience but I had a Mirena coil from 1998 (for contraception purposes) and before the menopause, I always had periods. However, my periods stopped while I was part way through my second Mirena coil and I wondered why. I thought perhaps the new coil had a slightly different formula but it transpired that I was post menopause. I remember the doctor saying that as I had always had periods before with the Mirena, there was no reason for them to suddenly stop other than the menopause and that is why I had the tests.
I then started using a 50mcg oestrogen patch with the Mirena coil still in place but I never had a period. I didn't find the 50mcg patch very effective and it clearly was not delivering enough oestrogen for my needs but I imagine that had I been using the oestrogen gel like I am now, I would probably have built up enough lining to have periods.
I don't know if that explains it.
Re the Mirena
The amount of progestogen needed to oppose oestrogen and prevent the lining thickening is dose dependent - so whether or not you get periods on Mirena is directly related to the amount of oestrogen in your system - either your own or from HRT. Those women with high oestrogen levels and heavy periods - will get lighter periods but they may not stop completely (while they are fertile).
As you get towards peri-menopause and in peri - your oestrogen levels will drop and therefore periods may well stop. However if your periods stop while using the Mirena - this absolutely does not mean you are post-menopause in fact it is most likely that you are not!! It means you are peri-menopausal - probably will be for a certain length of time which is impossible to determine - could even be a couple of years or more before being post-menopausal. Blood tests do not help because as we know the levels of FSH go into the post-menopausal range even very early in peri sometimes. We have had several examples of women on here being told they are post-menopausal on the basis of a single blood tests - or even several - and one women was told this after one missed period and that she would never have another period - which of course she did very soon!
So - you cannot date your menopause from periods stopping using the Mirena, nor from a blood test. You would have to stop using the Mirena and wait 12 months to see if you were post-menopausal or not!
Hurdity x