Sterilization is the most widely used form of birth control in the United States. Eleven million women rely on tubal sterilization as a means of contraception. Traditionally, this has meant tubal ligation — or having your tubes tied. But now the Essure procedure offers you an alternative to tubal ligation as a permanent form of birth control.

Essure is a device that resembles a tightly coiled tube or spring. It's small enough to be inserted into your fallopian tube — the pathway from your ovary to your uterus through which your eggs and your partner's sperm travel. The device works by blocking your fallopian tubes, thereby preventing your egg and your partner's sperm from meeting. That way you can't become pregnant.

The flexible coil measures 4 centimeters in length. It expands to a diameter of 1 to 2 millimeters once it's in place.

This flexible device is made from two kinds of metal — nickel-titanium and stainless steel — and polyester fibers. Once in place, the device uncoils to conform to the shape of your fallopian tube. The polyester fibers promote the growth of new tissue into and around the metal device. Eventually, this leads to scar tissue, which blocks your fallopian tube.

A potential advantage of this procedure is that, unlike tubal ligation, it doesn't require an incision. Placement of the device involves guiding an instrument through your body's natural passages. General anesthesia isn't usually needed.

To perform the Essure procedure, your doctor accesses your fallopian tubes through the opening of your uterus (cervix), which can be reached from your vagina.

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Placement of the Essure coil To perform the Essure procedure, your doctor inserts a coil into each of ... << ENLARGE

A few hours before the procedure, you take medication to help relax your muscles and prevent any muscle spasms while the coils are being placed. During the procedure, you may receive a local anesthetic to numb the area around your cervix. Your doctor guides a narrow instrument (hysteroscope) into your vagina and through your cervix into your uterus. The hysteroscope is connected to a video monitor so that your doctor can see inside your uterus to locate each of your fallopian tubes.

Once the hysteroscope is in place, your doctor passes a catheter through it to insert the tiny coil into each fallopian tube. Your doctor removes the catheter, and the coil remains in place.

The entire procedure takes about 35 minutes. It's usually performed in an outpatient setting, which means you'll go home the same day you have it done.

It's possible that your doctor may not be able to insert the device in both of your fallopian tubes on the first attempt. In clinical studies, one in seven women needed to have the procedure repeated.

It's also possible that your doctor might not place the coils in the correct position. This can happen if:

• The coils are placed too far up your fallopian tubes.
• The coils aren't placed far enough up your fallopian tubes.
• One or both of the coils break through the wall of your fallopian tube or uterus.
• The coils come out of your fallopian tubes after being placed there.

If the coils are in the wrong position or come out of your fallopian tubes altogether, you won't be protected against unwanted pregnancy.

No, the Essure procedure is permanent. Once the coils are implanted into each of your fallopian tubes, you would need a major operation to remove them. Even then, it may be impossible to have your fallopian tubes successfully opened. Before having this procedure done, be certain that you never want to become pregnant.

In clinical studies to determine Essure's effectiveness, researchers evaluated women two years after having the procedure done. They found that the device was effective 99.8 percent of the time in preventing pregnancy. However, it's difficult to know at this point how effective Essure will be in the long run. Because the device is new, long-term data aren't yet available.

It's not recommended that you have this procedure if you:

• Aren't sure you want to permanently end your ability to conceive in the future
• Have had a tubal ligation in the past
• Suspect you might be pregnant
• Have had a baby, a miscarriage or an abortion within the previous six weeks
• Have an active pelvic infection
• Have your uterus or your fallopian tubes in an unusual shape or position
• Have allergies to any of the components used in the device or procedure, such as nickel or the dye used for X-ray contrast
• Are unwilling to use backup birth control for the three months following the procedure

As with a tubal ligation, if you were to become pregnant after having the procedure done, you're at increased risk of an ectopic pregnancy — a situation in which the fertilized egg implants in a fallopian tube rather than your uterus.

More than likely, you'll be able to leave the medical facility shortly after your procedure is complete. Most women go home about 45 minutes after it's done. You can return to your normal activities that same day or within one to two days.

It takes about three months before the scar tissue develops to block your fallopian tubes. During this time, you'll need to use a backup form of birth control — anything except an intrauterine device (IUD).

After three months, you'll have a follow-up visit with your doctor to see if your fallopian tubes are effectively blocked. To find out, your doctor injects dye into your uterus and takes an X-ray to see if any of the dye moves beyond your uterus into your fallopian tubes. For some women, it can take up to six months for the tubes to be completely blocked. Upon learning that your tubes are blocked, you'll no longer need to use backup contraception.

No. Essure provides no protection against sexually transmitted diseases (STDs) , such as HIV/AIDS, genital herpes and gonorrhea.

Although prices for the U.S. market haven't yet been finalized, cost of the Essure procedure is expected to be around $2,500 — or roughly equal to the cost of a tubal ligation.

The Food and Drug Administration approved Essure for use in the United States in November 2002. The only limitation in its availability is the time it will take to train doctors to perform the procedure.

As with any form of birth control, there are advantages and disadvantages:

Essure can protect you against unwanted pregnancy for the remainder of your reproductive years. But its effects are permanent, so take the time to research all of your options in order to make an informed decision.