THE EVOLUTION of birth-control methods is all about increasing efficacy while minimizing user input. The more thought that goes into utilizing a contraceptive method, the more likely that method won't be used, or will be used incorrectly.

The longest-term, most user-friendly contraceptive method short of permanent sterilization is the intrauterine device, or IUD. IUDs are placed into the uterus in the doctor's office and can stay put for five or 10 years, depending on the type, without any real thought required.

But the IUD has gotten a bad rap over the years.

In the '70s, an IUD called the Dalkon Shield was taken off the market after women developed serious infections that resulted in multiple lawsuits. It was found that the design of the Dalkon Shield's strings increased the chances of serious uterine and pelvic infections.

An IUD is a T-shaped device with a string hanging from the bottom of the T. The T part of the IUD is placed inside the uterine cavity, while the string extends through the cervix (the opening to the uterus) into the vagina. This is so there is something to grasp when it's time for the IUD to be removed.

The Dalkon Shield contained strings whose design allowed easy passage of bacteria from the vagina, where bacteria are abundant, to the uterus, where they are not. This led to pelvic inflammatory disease, infertility and ectopic pregnancies.

Today's newer IUDs have been redesigned and no longer carry the same high risk of infection. However, the Dalkon Shield fiasco has left in its wake a lingering fear among many women that exists to this day.

Just because today's IUDs are safer does not mean they're for everyone, but they have become a good option for an increasing number of women.

The two most commonly used IUDs currently are the copper-containing IUD (marketed as Paragard) and the progestin-containing IUD (marketed as Mirena).

The copper IUD can stay in place for 10 years, while the Mirena IUD can be used for five.

Why, you may ask, would anyone choose a five-year IUD when they could have one that lasts for 10 years?