What is an IUD?
An IUD is a type of contraceptive (birth control). IUD stands for Intrauterine Device. This form of birth control can also be called an IUC (intrauterine contraceptive). An IUD is a reversible form of birth control.

What does an IUD look like?
IUDs that are available in the United States are T-shaped. The stem is about 1 inch long and the arms are each about 0.5 inches long. A thin thread is attached to the bottom of the T.

What are they made of?
There are two types of IUDs available in the United States. In both types, the body of the IUD is made of plastic (polyethelene). One type of IUD has a copper band around the stem and arms. This is called a copper IUD. The other type of IUD has a hormone contained in its stem where it is slowly released. The hormone is called levonorgestrel and it is similar to progesterone. The same type of hormone is found in most birth control pills.

How do IUDs work?
Fertilization refers to the binding of a sperm and egg. This normally occurs in the fallopian tubes. The fallopian tubes run from the ovary to the uterus. Following fertilization, the fertilized egg begins to travel along the fallopian tube and into the uterus. As it travels, it undergoes several rounds of division. The growing mass of cells is called an embryo. The embryo then enters the uterus (womb) and implants into the wall of the uterus where it will grow until the time of delivery.

The exact mechanism of action of IUDs is not known. However, IUDs seem to prevent pregnancy from occurring by acting at several steps along the processes. For example, it appears that IUDs prevent sperm from reaching the egg. IUDs may also prevent the embryo from implanting. IUDs do not appear to disrupt a pregnancy after it is growing inside the uterus- that means they are not considered to be abortifactants.

 [READ: Understanding the Risks of Contraception]

Why is there a thread attached to the IUD?
The thread is helpful to help your doctor ensure that the IUD is in the correct position (as will be explained below) and to help remove the IUD when it is time to take it out.

How is an IUD inserted?
An IUD is inserted in a doctor's office. The woman lays on the examination table with her heels in foot-holders. A speculum is placed in the vagina to allow the doctor to visualize the cervix. A soap-like solution is then used to clean the outside of the cervix. Sometimes a clamp (tenaculum) is placed on the cervix to help the doctor hold the cervix and position the uterus. A thin piece of plastic or metal is then passed through the cervix and into the uterus. This allows your doctor to determine the path of your cervix and to measure the depth of your uterus. The doctor then uses this information to place a narrow tube containing the IUD into the correct position inside the uterus. The IUD rests inside this tube with the IUD arms folded. The IUD is then released from the tube into the uterus and the IUD arms extend open. The tube that carried the IUD is then removed leaving behind only the IUD and the tailing threads of the IUD that come out of the cervix. The threads are then cut so that about 1.5 inches of the threads are left outside of the cervix and within the vagina.