Since the copper IUD / copper chain does not affect your cycle hormonally, ovulation continues to occur, which trackle can recognise and evaluate. But please pay attention very closely whether you can still see distinct changes in the quality of your cervical mucus – if the mucus does not change cyclically, trackle is not able to evaluate an ovulation.

Do you have a hormonal IUD? Then be sure to check this article:

Can I use a (hormonal) IUD in addition to trackle?