What is the Mirena IUS?

The Mirena IUS is essentially an intrauterine device, or IUD. Its manufacturer calls it an “intrauterine system” because it stops sperm from fertilizing an egg like an IUD, and it stops a fertilized egg from implanting in the uterus. Otherwise, the device is the same T-shape and size of a standard IUD. That is why we use IUS and IUD interchangeably when referring to it.