During a ultrasound exam I was told that I have a thickening of the endometris wall and will need a biopsy to determine how serious it is. What is it and what causes it?

It is thickening of uterus wall and caused due high amount of estrogen, you should do biopsy to get detail analysis. There could be other reasons for the thickening.

It is NOT only caused by excess hormones - please research your answers more carefully.