zen you may have seen my threads but I am being pressurised to have a biopsy and my lining is 5mm. Yours would be described by my drs as thin , mine was at 4 mm previously. I like you don't know what to do, though I would be very tempted to do as 7dwarfs suggested and be monitored though scans. Just wanted to say good luck and let us know how you get on.