Having pregnancy with an IUD can increase the chances of miscarriage but pregnancy after IUD if progresses to a miscarriage then IUD cannot be held responsible. You should try for conception again and get a detailed evaluation done from a gynecologist to rule out any other causes of threatened miscarriage.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I had a miscarriage after an IUD expelling itself. However, I did become pregnant after sivery