Can totally understand you wanting to 'embryo bank' now so that you don't have the stress of needing to repeat IVF down the line when you are older and the chances are lower, especially if you are now already only collecting 3 eggs per cycle. I had 11 IVF attempts, of which 7 went to egg collection and after my first few cycles, I started having exactly the same issue as you - that I would have several decent size follicles but only a couple of mature eggs. I had one cycle where I injected the trigger at an angle based on instructions I got with the trigger that were not given to me previous cycles. It hurt like hell going in and I had a big hard lump which perhaps was the trigger medication just sitting there and not getting into my system to make my eggs mature, as that cycle I only got 1 mature egg from 8 mature follicles. I think it was my second last cycle that the trigger went smoothly and after having read a study (which I can't find now) showing that women with normal weight range had hCG levels about 350 at 12 hours post trigger compared to obese women having levels at only about 150, I decided to test my hCG levels 12 hours after my trigger. Surprisingly my results were only 140 even though I was not in the obese category. I mentioned my concerned to my IVF Dr, and she said I could take the Synarel nasal spray in addition to the hCG trigger, to purge my brain of it's own FSH/LH hormones in addition to the trigger. My last scan on day 15 of my last and finally successful IVF cycle showed 19 18 15 13 10 10 and 4 less than 10mm, and I got 4 mature eggs on day 18 EC so at least my mature follicle count and number of mature eggs were in sync.
Also like you, we both seem to be research orientated as a way of working through our IVF journey. Not many others know about premature progesterone rise in an IVF cycle causing the lining to be out of sync and reducing implantation success. According to a few studies I read like this one, premature progesterone rise only has a detrimental effect if the embryo is transferred on day 3 but no effect if day 5 transfer is performed, which I guess makes sense as in a natural cycle, the embryo would still be travelng down the fallopian tube and not yet exposed to progesterone on day 3. I had a very empathetic acupuncture Dr who would give me as many blood tests as I wanted so I could get my blood tested the day before and the day of trigger to compare and see if my progesterone did prematurely rise in order to help me make a practical decision about day 3 versus day 5 transfer rather than just wondering and worrying.
You say that 'at your age' 50% of the embryos won't be viable. Is it rude to ask how old you are? It is amazing that you managed to get 4 hatching blasts frozen from 3 IVF cycles of producing only 3 eggs per cycle. I wish you well with your upcoming NHS cycle. Will be interesting to see how it compares to the treatment you received privately. Will the protocols be any different? Love to hear how you get on if you have the strength to come on here and update. xox.