**Core Concept**
Third-generation intrauterine contraceptive devices (IUCDs) are a type of long-acting reversible contraceptive that utilizes a hormone-releasing mechanism to prevent pregnancy. These devices release progestin hormones, which alter the uterine environment to inhibit implantation of the fertilized egg.

**Why the Correct Answer is Right**
The mechanism of action of third-generation IUCDs involves the release of progestin hormones, which induce endometrial atrophy and alter the cervical mucus, making it difficult for sperm to penetrate. The progestin hormone also affects the endometrium, making it inhospitable for implantation of the fertilized egg. This results in a high efficacy rate of up to 99% in preventing pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the type of IUCD. There are different types of IUCDs, and this option does not provide any information about the mechanism of action or the type of hormone released.
**Option B:** This option is incorrect because it does not accurately describe the mechanism of action of third-generation IUCDs. The primary mechanism of action of these devices is the release of progestin hormones, not the release of estrogen.
**Option C:** This option is incorrect because it does not provide any information about the mechanism of action or the type of hormone released by third-generation IUCDs.

**Clinical Pearl / High-Yield Fact**
Third-generation IUCDs are a highly effective form of contraception, with efficacy rates comparable to surgical sterilization. They are also reversible, making them a good option for women who want to delay childbearing or have not yet achieved their desired family size.

**Correct Answer:** C.