Hi Sunnydays and Pollie
Not sure I can answer these Qs!
Fron what I've read - progesterone changes an "oestrogen primed endometrium" from proliferative to secretory and then the fall in prog triggeres the bleed. Also though if you are taking oestrogen, if you are taking sufficient progesterone at the same time, the prog intereferes with the oestrogen receptors ( I presume it binds to them?) to prevent the lining building up - the prinicple behind continuous combined HRT. Quite what this means in terms of the structural layer of the uterus I don't know! I mean I don't know if it is actually secretory - because the lining doesn't build up - I would presume not??? I have tried looking this up but can't really find the info.
Also progestogens have the ability to thin the lining of the uterus (after it has been stimulated to grow by oestrogen) without it being shed - and there is research to show this. I presume this is why some women do not bleed even on sequi HRT?
Re your Q Pollie - again I can't say exactly (I don't know!) but I would suggest not, because if (the prog) it is doing its job and the lining is kept thin despite being also stimulated by oestrogen, then even though you increase the prog and then reduce it, there should be nothing to shed. If you have too much progestogen compared to oestrogen on a continuous basis though this can overthin the lining causing ulceration and some spotting/bleeding - which is what happens to some women using the Mirena especially if they go into menopause and aren't also taking oestrogen.
This is all from my head/memory so apologies if it sounds a bit imprecise.
Hurdity x