Thanks for your query.
Normal endometrial thickness is 4-10mm in reproductive age group.
Endometrial thickness increases slightly if you are on estrogen
but not as high as 16.9mm.
Cause of increased endometrial thickness could be endometrial hyperplasia
. It could be typical or atypical type.
I suggest you to get a hysteroscopic biopsy
done for definitive diagnosis.
Treatment depends on the diagnosis.
Hope this helps.