Evolution and functional differences of intrauterine devices

1. Lippes Loop (Non-Medicated / Inert IUD)

Introduced in the 1960s, the Lippes Loop is a classic example of a first-generation, non-medicated IUD. It is a double-S-shaped loop made of polyethylene (plastic) impregnated with barium sulphate so that it can be seen on X-rays.

• Mode of Action: It relies entirely on its physical presence – acts as a mechanical foreign body, inducing a sterile, localized inflammatory response in the uterine cavity. This alters the uterine fluids, attracting macrophages and polymorphonuclear leukocytes, which phagocytose (engulf and destroy) sperm cells, preventing fertilization.
• Key Characteristic: It contains no active chemical or hormone. It is rarely used in modern clinical practice today due to higher expulsion and failure rates compared to newer generations.

2. Copper-Releasing IUDs (Medicated / Second Generation)

Examples include the Cu-T and Multiload-375. These feature a plastic T-shaped frame wrapped with copper wire or sleeves.

• Mode of Action: In addition to the mechanical foreign-body effect, these devices continuously release copper ions (Cu²⁺) into the uterine environment. Copper ions are highly spermicidal; they suppress sperm motility, alter sperm metabolic enzymes, and destroy the acrosome, making it impossible for the sperm to fertilize an egg.
• Key Characteristic: Highly effective (up to 10 years) and completely non-hormonal, making them ideal for women who wish to avoid synthetic hormones. They can cause heavier or longer menstrual periods, particularly in the first few months.

3. Hormone-Releasing IUDs / IUS (Medicated / Third Generation)

Examples include Mirena, Progestasert and LNG-20. These feature a T-shaped cylinder that slowly and steadily releases a synthetic progestin called Levonorgestrel (LNG) directly into the uterus.

• Mode of Action: While they still evoke a minor foreign-body reaction, their primary efficacy comes from the hormone. The local release of levonorgestrel drastically thickens the cervical mucus, creating an impenetrable barrier for sperm. It also thins the endometrial lining, preventing any chance of implantation, and can partially suppress ovulation.
• Key Characteristic: Instead of increasing menstrual bleeding like copper IUDs, hormone-releasing IUDs significantly reduce menstrual blood flow and cramping (often resulting in light periods or complete amenorrhea), making them a common treatment for menorrhagia (heavy periods).