**Core Concept**
The question requires knowledge of contraceptive implants, which are long-acting reversible contraceptive methods (LARCs) that release hormones to prevent pregnancy. These implants are designed to be inserted under the skin and can remain effective for several years.

**Why the Correct Answer is Right**
Mesigyna is a type of injectable contraceptive, not an implant. It is a combination of estradiol enanthate and norgestrel, administered via intramuscular injection every 28 days. This is in contrast to the other options, which are all types of contraceptive implants.

**Why Each Wrong Option is Incorrect**
**Option A:** Norplant is a type of contraceptive implant that releases levonorgestrel. It consists of six small rods that are inserted under the skin of the upper arm and can remain effective for up to five years.
**Option B:** Implanon is another type of contraceptive implant that releases etonogestrel. It is a single rod that is inserted under the skin of the upper arm and can remain effective for up to three years.
**Option C:** Jadelle is a type of contraceptive implant that also releases levonorgestrel. It consists of two rods that are inserted under the skin of the upper arm and can remain effective for up to five years.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that all contraceptive implants require a healthcare provider to insert and remove them, and they can be effective for several years, making them a convenient and long-lasting option for women who want to avoid pregnancy.

**✓ Correct Answer: D. Mesigyna. Mesigyna is an injectable contraceptive, not an implant.**