Description
The IUD is a small T-shaped device, with a string at the base of the T, inserted into the uterine cavity. There are two types of IUDs, copper and progesterone-releasing. A copper IUD can remain in place for up to 10 years. In the progesterone-releasing IUD there is a reservoir of progesterone that is slowly released and becomes exhausted after one year. Once exhausted the IUD must be replaced, which means a new one is required annually. Women who have a heavy flow or dysmenorrhea may tolerate or even benefit from the progesterone-releasing IUD, which can reduce menstrual bleeding.

An IUD prevents fertilization by triggering an inflammatory response in the endometrium.

In plain english, this means that an IUD hampers the ability of sperm to pass through the uterine cavity and thus disrupts the reproductive process. Progestin-releasing IUDs also thicken the cervical mucus and changes the endometrial lining, making the uterus unfavorable for implantation.

Effectiveness
The IUD is approximately 99% effective.

Directions
A qualified medical practitioner will properly insert the IUD. Under no circumstances should a woman attempt this on herself or have an unqualified person attempt the insertion on her.

Drawbacks
IUDs can increase menstrual flow and cramping, which may be particularly severe in the first few months after insertion. Also, there is the possibility of spotting between periods and a small minority of women expel the IUD during the first year of use. Also, there is no protection from STDs.