Final answer:
The device used to prevent pregnancy for up to 3 years, placed under the skin of the arm, is known as an implantable rod, with the brand name Implanon. It releases the hormone progestin to prevent pregnancy.
Step-by-step explanation:
The device placed under the skin that releases time-released hormones to prevent pregnancy for up to 3 years is known as an implantable rod. Specifically, one brand name for such a device is Implanon. This matchstick-sized, flexible rod is inserted under the skin of the upper arm and it works by releasing a hormone called progestin. Progestin brings about changes in the uterus lining and the cervical mucus to prevent sperm from joining an egg, and in some cases, it may also stop the ovaries from releasing eggs.
It's important to note that timing is crucial when starting birth control methods containing hormones after giving birth. Women should generally wait three weeks after giving birth before initiating methods that contain both estrogen and progestin due to the increased risk for blood clots. Those with additional risk factors such as obesity, history of blood clots, smoking, or preeclampsia, or those who had a cesarean section, should wait six weeks. The hormonal method of contraception, which includes the implantable rod, is one of the most reliable with a failure rate of less than 1 percent when implanted correctly.