escher: Pokey is correct, one of the things they are looking for with estradiol is its correlation to the number and maturity of follicles. This is particularly important if you are using a trigger shot. You don't want to trigger before the follicles are mature. For every 18mm follicle estradiol should be around 250. As the follicles mature, that number goes up.
For example, on CD 12, I had estradiol of 339 with two follicles -- one at 12mm and one at 14. This was a medicated cycle with clomid 50mg.
CD14, Estradiol was 421 and I had one follicle on the right side that went from 6mm to 12mm and the lead follicle on the left went from 13 to 15.5mm
CD15 Estradiol was 565, and at that point I had 1 mature follicle at 18.5mm , one at 12.5mm and one at 15.5mm. This is the night that I triggered. The assumption being that the 15.5 would fully mature to 18mm in the following 36 hours.
I know they also monitor estradiol if there are cysts present on CD3. If estradiol is high at this point, ovulation is not likely and the cycle is delayed until the next period, when usually, the cyst resolves on its own.
I believe it also correlates to uterine lining thickening.
Good luck! I hope you find some answers soon. <3
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