I'm with NUH. According to my gynae, the vagina insert usually do the trick quite well, but I didn't increase at all for 7-8 days with 2mg, finally he increased to 4mg, then 3 days later it increased to 9mm with triple layer. I'm not sure is it because I don't respond to oral progynova, or I'm just taking longer to build up the lining as my cycle can go up to 40 days, or because of my acupuncture with TCM, but I am glad I persisted to wait for it to go up more before the transfer, I failed my first FET with 7mm, and was very ready to give up this cycle if it stays on at 7mm only. If your lining is not ready then better don't waste the embryos. My TCM told me usually must be 8mm and above safer.