I believe the first reason for an failed IVF is the quality of the embryos.
I got pregnant with my 1st cycle, and my embryos were good quality at this time, on my second cycle, they did not do as good, they were slower to develop and I believe that it is why the cycle failed.

I am still in my 2ww, but from what I have been told it exactly what mathilde said, plus it could be an implantation problem. Since I over stimulated and coasted without my meds for a while, I know that can impact the quality of the eggs. Fingers crossed that at least one makes it.

Mine just didn't take. No other reason. I believe it just wasn't the right time.I have grown spiritually since then..2yrs ago.

My RE did not give me a reason for why it failed. Maybe b/c my E2 was low the day of ER. It just didn't work. I am sure if it continues to not work they will go in and do more tests. Sometimes it just takes several tries. I pray this cycle is THE ONE for us though! :-)

I was in the same boat as Rachm, I also coasted before ER because of elevated E2. We had 19 eggs, 12 mature, and only 1 made it to a blastocyst. The other morulas (4 day embies) and 4 were never good to begin with. Anyway, we implanted 1 blastocyst and 1 morula. I've heard of women getting pregnant with morula's. But you just never know..I know one thing I've learned is that infertility is still a very complex issue and there are so many unanswered questions even doctors can't answer. Good luck!!

I personally do not have experience with this but from what I understand, it can be a few things but really depends on the individual and what there situation is, poor embryo quality and/or a lining that is too thin can cause a failed IVF.