Has anyone ever passed a uterine cast??

Hi ladies, I’ve had really heavy bleeding this morning (in middle of period) then a few hours later passed what I think is a uterine cast. This has happened before about 5 years ago and since had surgery to remove polyps from my womb. Got a bit of a shock this morning when it happened again. Has anyone experienced this and have any ideas what this means? I’m currently trying to conceive, have been since Dec 17. Had a MC in June 18 at 7 weeks and currently awaiting investigative surgery into constant spotting, lack of ovulation, possible endo. Xx