**Core Concept**
Intermenstrual bleeding is a type of abnormal uterine bleeding that occurs between menstrual periods. It can be caused by various factors, including hormonal imbalances, uterine abnormalities, or the use of certain medications.

**Why the Correct Answer is Right**
The correct answer is **Levonorgestrel-releasing Intrauterine System (LNG-IUS)**, also known as Mirena. LNG-IUS is a type of hormonal intrauterine device (IUD) that releases a small amount of the synthetic progestin levonorgestrel. This hormone helps to thin the uterine lining, reducing menstrual bleeding and preventing pregnancy. As a side effect, LNG-IUS can cause intermenstrual bleeding, also known as breakthrough bleeding, which is more common during the first few months of use.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, please choose one of the other options.
**Option B:** Progesterone-only pills (POPs) are not commonly associated with intermenstrual bleeding as a frequent side effect. While POPs can cause irregular bleeding, it is more often in the form of prolonged or heavy menstrual bleeding.
**Option C:** Combined oral contraceptives (COCs) can cause irregular bleeding, including intermenstrual bleeding, but it is not as common as breakthrough bleeding with LNG-IUS.
**Option D:** This option is not provided, please choose one of the other options.

**Clinical Pearl / High-Yield Fact**
It's essential to note that intermenstrual bleeding can be a sign of an underlying medical condition, such as endometrial hyperplasia or cancer. Therefore, any new or persistent abnormal bleeding should be investigated and managed by a healthcare provider.

**Correct Answer:** C. Combined oral contraceptives (COCs) can cause irregular bleeding, including intermenstrual bleeding, but it is not as common as breakthrough bleeding with LNG-IUS.