**Core Concept**
The etonogestrel implant (Implanon) is a long-acting reversible contraceptive device that releases a steady dose of etonogestrel, a progestin hormone. To maintain its contraceptive efficacy, regular follow-up appointments are necessary to assess its placement and function. The device's lifespan and replacement timing are critical factors in its use.

**Why the Correct Answer is Right**
The etonogestrel implant is designed to be effective for up to 3 years. After this period, its contraceptive efficacy may decrease due to a gradual decline in hormone release. Regular follow-up appointments are essential to assess the device's placement and function. If the implant is still in place after 3 years, it is recommended to be replaced to maintain its contraceptive efficacy. This replacement timing allows for optimal hormone levels and effective contraception.

**Why Each Wrong Option is Incorrect**
**Option A:** 2 years is too early for replacement, as the device is still effective within this timeframe.
**Option C:** 4 years is too late, as the device's efficacy may have decreased significantly by this point.
**Option D:** 5 years is not a recommended replacement interval, as the device is no longer considered effective after 3 years.

**Clinical Pearl / High-Yield Fact**
It is essential to schedule regular follow-up appointments to assess the etonogestrel implant's placement and function, as its efficacy may decrease over time.

**✓ Correct Answer: B. 3 years**