[SoothingDave]

There are 2 types of IUDs, one is copper and the other progesterone releasing both of these act as spermicides, so IUDs while they do prevent implatation will also prevent conception.

How does the IUD owner/user know which method was used to prevent a pregnancy?

SD

[underthesun]

Unfortunately you don't but conception is not very likely with either. It is very effective.