An intrauterine device, or IUD, is nearly 100-percent effective when it comes to pregnancy prevention. Like all contraceptives, however, it is not foolproof. According to Dr. Erika Nichelson, an obstetrician/gynecologist with Mercy Medical Center in Baltimore, it is possible to become pregnant with an IUD in place. “The chance of that is approximately 1 percent, and often occurs because the IUD is not in the proper place, but has shifted down to the cervix," she said. A doctor must insert an IUD, but you can check to make sure that it’s in place by feeling for its string. Call your doctor if you cannot find the string, as the device may have shifted from the uterus.