How do intrauterine devices prevent embryo implantation or release hormones for contraception?

SouravNovember 13, 2024

Answered step-by-step

Intrauterine devices (IUDs) are highly effective forms of contraception that work primarily by preventing fertilization and, in some cases, altering the uterine environment to inhibit embryo implantation. There are two main types of IUDs: copper IUDs and hormonal IUDs, each with distinct mechanisms of action.

Copper IUDs

Mechanism of Action

1. Sperm Inhibition: Copper IUDs release copper ions into the uterine cavity, which create a toxic environment for sperm. These ions interfere with sperm motility and viability, making it difficult for sperm to reach and fertilize an egg.
2. Foreign Body Reaction: The presence of the IUD induces a localized inflammatory response in the uterus, which further disrupts sperm function and can prevent fertilization. This reaction may also affect any embryos that may form, as the inflammation can hinder their ability to implant successfully.
3. Altered Uterine Environment: The copper ions change the fluid composition in the uterus and fallopian tubes, making them inhospitable to sperm and potentially affecting ovum transport.

Hormonal IUDs

Mechanism of Action

1. Hormonal Release: Hormonal IUDs, such as those containing levonorgestrel, release a small amount of progestin into the uterus. This hormone works through several mechanisms:
   • Thickening Cervical Mucus: Progestin thickens the cervical mucus, which obstructs sperm passage into the uterus.
   • Inhibition of Ovulation: Although not the primary mechanism, hormonal IUDs can suppress ovulation in some users by affecting hormonal signals from the ovaries.
   • Endometrial Changes: Progestin alters the endometrial lining, making it less receptive to a fertilized egg, thus reducing the chances of implantation if fertilization occurs.
2. Local Inflammatory Response: Similar to copper IUDs, hormonal IUDs also create a foreign body reaction in the uterus that may interfere with embryo implantation by altering the uterine environment