OP here. Thank you all for your replies. I had an HSG done that was normal but it was a while ago so maybe I need another one. I had a total thyroidectomy done in 2010 so I check my TSH regularly. Unfortunately, I learned how this can affect pregnancy too late. When I became pregnant naturally in 2013, my obgyn told me that I didn't need to change my synthroid dose for a while so I didn't have my levels checked until 8 weeks and by that time my TSH had spiked and we lost a heartbeat two weeks later. I started seeing a new endocrinologist when I began doing IVF and she keeps a close eye on my levels now. To the poster who mentioned natural cycle, I found it interesting that you supplemented with progesterone only, I asked about doing that but was told their protocol is to use both estrogen and progesterone. All along I have been doing "natural cycle" FET's, but once I ovulate, they said I had to take estrogen and progesterone until the beta. They're checking my E2 levels during monitoring and on the day of transfer so I guess they must feel I need the estradiol but I always hate taking it because it can bind to T4 (synthroid) and on my 2nd failed FET, my TSH went from 1 to 17 after just 10 days of estradiol. Now I have to increase my Synthroid as soon as I start taking it and check my TSH every week.

Also, as to PP, if she is transferring frozen embryos, it doesn't matter if her tubes are blocked -- unless she is doing a natural cycle. Though you might want to do a saline sono to make sure that you don't have any polyps in your uterus. That can change over time -- even within 6 months.

I would definitely get the implantation window biopsy (ERA or Yale EFT). I had 3 failures with CGH normal DE embryos on the standard estrogen / progesterone protocol. I thought the artificial estrogen / progesterone might be messing with my implantation. I did the EFT test based on a natural cycle: no estrogen and just progesterone suppositories. EFT was normal on the natural cycle, so we did my next transfer with a natural cycle protocol - transfer on day 5. I finally got a pregnancy that has stuck (so far to 20 weeks), but even then I seemed to be a late implanter. The urine FR response tests that had always been reliable in the past for me showed negatives. I didn't go in for my beta until late, but it was finally positive.

Also you should think about making sure your Vitamin D levels are normal, think about immune testing and treatment (at least prednisone), check for any clotting disorders, and make sure your TSH is below 1, and then re-check at the time of the beta as it can rise rapidly.

Have you had an HSG recently? Within the last 6 months? I agree that your implantation window could be off but checking to be sure you don't have any blockages in your tubes is important. Over time, things can change in there - speaking from experience with failed PGS embryos...and now a 28 week pregnancy on the way. I had not had a repeat HSG since having baby #1.

I would get the ERA biopsy done. I believe some women need an extra day of progesterone and some even need 2 extra days. I think I read that 25% of the ppl who have the test done come back as pre receptive (need more progesterone)

Thank you! I just read it, looks like I'll have to wait a bit longer to see what the outcome is. Hopefully seven days past ovulation is the answer for those posters and for me as well.

Check the "ERA Biopsy" thread.

I've had 3 FET's with PGS tested embryos that all failed to implant. Endometrial biopsy revealed no problems with my uterus so there's no clear explanation for why implantation isn't happening. I had decided to give up figuring that IVF just doesn't work for everyone but my doctor suggested one last try. He wants to transfer 7 days past ovulation instead of 5 days past as we had been doing. He said some patients with recurrent implantation failiure need to delay the ET for 2 additional days to allow for the implantation window to mature. Has anyone else tried this and if so, what was the outcome? Thanks!