Far - I saw an obstetrician before I did ivf (which failed, this is a natural bfp miracle) as there will be complications for birth due to other health issues and she recommended aspirin, but I didn't like to take it due to ivf drugs etc. Then after ivf failed we paid for the Immune level 1 and level 2 tests (gp did a few of level 1 basic ones for us) and one of the early results showed I had a blood clotting issue, which is quite common and the treatment for it was aspirin and/or clexane injections (injections if do ivf or get a bfp) so I started the aspirin whilst queing to see one of the top reproductive immunologists to go over our results and give us a treatment protocol.
We saw, privately, Dr George Nduwke (consultation included in cost of tests which were £1600, but we did every single immune test necessary!) - he has just started a new clinic in Central London, but we saw him at the Care clinic where he was Medical Director before he moved. He is now working alongside Zita West (google her clinic for details, but you can just see him and avoid wasting time on what she does etc etc). He specialises in immune issues that cause implantation failure and repeat miscarriages. Other dr's that are well known in this field are Dr Gorgy and Dr Taransai - one based at ARGC which is an IVF clinic also if I remember rightly. Dr N was so happy it was a natural bfp for us, he wrote all the private prescriptions I needed (as lots of issues picked up by tests) to try and maintain bfp and wrote to my gp to get as much on nhs as possible (got all but intralipids and pessaries from my gp after 8 weeks). Obviously had to pay an admin cost for his time, as not doing ivf - but this included a scan and letters to my gp and prescriptions as well as seeing him once more.
I knew after 7 years of no contraception, over 36 months of serious ttc and no implantation and ivf failure there was something else wrong. We went down immune testing as I have one autuimmune issue already and it made more sense than doing chromosome testing of my eggs etc as no indication that was the issue for us.
Sorry for essay Far- if you have had 3 miscarriages the NHS will do basic miscarriage tests, which are some of the immune tests. They will not do all level 1 and 2 tests. Dr N tends to be seen as fairly conservative in treatment, which suited us rather than the more aggressive treatments of Dr Gorgy for instance. The NHS should also check if you have blocked tubes, issues with fibroids etc and healthy uterus, no STI's etc all of which can cause miscarriage issues. We had all those checks first and all were ok, on NHS. My issues were:
blood clotting issues - Factor V and PAI-P
thyroid too high for Dr N (he wants it below 2 for maintaining pregnancy, NHS ignores that and says it is ok)
Raised NK cells - 2 types
Basically I couldn't implant and then if I did I would reject any foreign matter in me due to my NK levels. I needed: aspirin, clexane, presnisilone, utrogestran, intralipids to week 12, plus the levothyroxine - 2 of these meds I carry on till birth the rest I have stopped now as the placenta takes over.