i just had a cyst out but part of my ultrasound results said i had a 1.4-2 cm endometrial thickening. the er doc who did the ultrasound seemed like an idiot to me and said it needed to be investigated.
but: my gyn/oncologist who removed the cyst was unconcerned; for premenopausal women, there is no upper limit and he says that yes, it gets very thick before your period.
A little thick but if you were about to get your period, that could explain it. That's why they wanted correlation. If you got your period right after and the measurement dropped to the low single digit mm it's fine. Kinda thick but it doesn't it's cancer. Most of the time it's hormonal.
I don't know about the complex part -- ask your doc. It sounds more like the way they take the measurement. It makes sense that it would thicken more before your perod.