When the implant was removed the mystery became clear - she had been given a dummy model.
Jessica Lindberg, who lives in Gothenburg, was only 16-years-old when she became pregnant.
The pregnancy was only discovered after 20 weeks when Lindberg approached her local clinic to get the implant removed and staff informed her of her condition.
"Then she says that this is presumably a test implant that you have had inserted. It is not a real contraceptive implant," the girl told Uppdrag Granskning, a television program on Sveriges Television broadcast on Wednesday.
A real contraceptive implant is white, while the dummy model is blue. This has raised the question of how the mistake could occur.
Both the National Board of Health and Welfare (Socialstyrelsen) and the public health disciplinary board (Hälsö- och sjukvårdens ansvarsnämnd - HSAN) have reviewed the case, but neither has managed to develop an explanation.
According to the pharmaceutical firm which manufactures the implants, there is no risk that the dummy models can be mixed up before they are handled by the clinic which operates them in.
The young couple are now the parents of a two-year-old boy. The couple's insurance company has rejected their claim for compensation arguing that "no one has been hurt".
A contraceptive implant is a small stick containing the hormone progesterone which is inserted under the skin in the arm. The hormone is slowly released into the body, preventing eggs from being released. Each implant lasts for three years.