According to a 2012 study by the Washington University School of Medicine in St. Louis, birth control implants have a failure rate of less than 1 percent. That means that in any given year, fewer than 1 percent of people who use birth control implants correctly will get pregnant.
The birth control implant is one of the most effective forms of birth control. With perfect use, fewer than 1 percent of people using the implant will become pregnant during any given year. This means that of every 1,000 women who use the implant, fewer than 10 will become pregnant each year.
A 2008 contraceptive study cited in Contraceptive Technology corroborated the 2012 study by the Washington University School of Medicine. This study indicated that the birth control implant prevented pregnancy in 99.5 percent of cases for both perfect and typical use. In this case, "perfect" use means using the implant precisely as designed, and "typical" use means using the implant as the average person uses it. In both cases, the implant was 99.5 percent successful.
It is possible to get pregnant while using the birth control implant, but it is highly unlikely. Implant manufacturer Implanon also notes that overweight women may have higher rates of implant failure and accidental pregnancy.