@hopefulhel so at age 35 the chance of an aneuploid embryo is 50%, at 38 it would expect it to be higher. Overall clinics usually advise the chance of a cycle being successful with an untested embryo to be 1 in 3. So at this point statistics are on your side.
However I was in a similar position, at age 35 I had never had a BFP and my fresh cycle yielded 9 high quality blasts. After the 2nd transfer I insisted on further investigations because the situation made no sense. The first thing we did was Pgt-A tested the embryos, 83% of the embryos came back euploid, so on every objective test I had high rates of high quality embryos, but they never implant.
So we went into recurrent implantation failure test, I’ve had:
Recurrent implantation blood tests, this is a thrombophilia screen and autoantibodies - I had no autoantibodies, I had a PA1 mutation (prone to clot so I'm now on aspirin and heparin), MTHFR mutation (I take methylfolate now).
Era Emma Alice - pre receptive and microflora issues. I would highly recommend this as this seems to be the most abnormal thing I’ve had and microflora is really important.
Hsg - normal, I would recommend some form of imaging, either a saline scan or hsg.
Hysteroscopy - cervical stenosis found and treated, but wouldn't explain the lack of success. This should only be done if there is a reason to do it.
Nk biopsy - this is quite controversial but after you’ve done everything else it might be worth exploring if things still don't work.
Essentially it’s up to you whether you chose to do further investigations at this point or try more transfers. You could start with Pgt-A and if you wanted to, then to explore further I would go for some form of imaging (hsg and saline scan) and the ERA EMMA ALICE (we have a thread on here about this test).