**Core Concept**
The expulsion rate of an Intrauterine Device (IUD) refers to the percentage of women who experience the device being dislodged or expelled from the uterus. This can be due to various factors, including incorrect placement, uterine size, or patient movement. A lower expulsion rate indicates a more stable and secure placement of the device.

**Why the Correct Answer is Right**
The expulsion rate of IUDs varies depending on the type of device and the population being studied. However, the lowest expulsion rate is typically observed with the _Mirena_ (levonorgestrel-releasing intrauterine system). This is because the _Mirena_ has a unique T-shaped design that provides a stable anchor within the uterine cavity, reducing the likelihood of expulsion. The hormone levonorgestrel also helps to thicken the cervical mucus, making it more difficult for the device to be dislodged.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify the type of IUD, making it a vague and unreliable choice.
**Option B:** This option is incorrect as it is not a recognized IUD with a low expulsion rate.

**Clinical Pearl / High-Yield Fact**
When counseling patients about the use of IUDs, it is essential to discuss the potential for expulsion and the importance of follow-up appointments to ensure proper placement and maintenance of the device.

**Correct Answer:** C. Mirena (levonorgestrel-releasing intrauterine system)