progesterone back up

I would like to know why on this 2nd cycle with donor eggs I have gone from natural cycle with progesterone pessaries 400 mg once a day to artificial thaw cycle with Prognova twice daily since day 5 and will be starting progesterone pessaries 400mg twice a day on day 16 two days before FET. I am 47.  I have had my scan on day 12 and my endo was at 8mm.  So FET will be 6 days after scan.   Apparently my endo could get up to 10 or 12 mm?  I would like to think that all this extra is to so that there is no room for error?
Any advice on this greatly recieved!

[Elaine Brown, MD]

Hi!
Yes, the normal endometrial thickness at the time of ovulation is about 11 mm.
Progesterone also functions to support the pregnancy, should it occur, until the placenta can grow and produce its own progestereone.
Be sure to ask your RE his/her thoughts about the change in dosage!  His/her nurse probably knows the answer too if you ask.
Good luck -- I hope it works!
Dr B