How Does an IUD Work?

Copper IUD

A T-shaped device that is inserted into the woman's uterus, the copper IUD slows the sperm's movement to the fallopian tubes, thereby impeding fertilization. According to the Mayo Clinic, the slowly released copper also inactivates the sperm while in the cervical mucus as well as preventing a fertilized egg from attaching to the wall of the uterus. The copper IUD has an effectiveness rate from 99.2 to 99.4 percent, and may remain in place for as long as 10 years.

Hormonal IUD

The hormonal IUD is the same shape and form as the copper IUD; the difference being it releases progestin instead of copper. Progestin slows sperm mobility while thinning the uterus wall, making it unsuitable for impregnation. The shape of the IUD slows the sperm's movement to the fallopian tubes to prevent fertilization. If an egg should become fertilized, the IUD inhibits pregnancy by preventing attachment to the wall of the uterus. The effectiveness rate of a hormonal IUD is 99.9 percent, and the device may be left in place for up to five years.

Health Risks of an IUD

The Mayo Clinic states that there are common side effects of the copper IUD, including menstrual pain and increased vaginal bleeding. The hormonal IUD typically decreases the menstrual flow, with some women having unpredictable flows and some having no flow at all.

Medical insertion of an IUD may cause a pelvic infection within three weeks of placement. An IUD does not protect the woman from sexually transmitted diseases, and spontaneous expulsion is a risk.