It does say that the baby's and the mother's health could be in danger, but where does it say it's often life threatening?

Never heard about an IUD failing at all so thanks for the link anyhow

It says that with an IUD if you get pregnant it's more likely that it will be an ectopic pregnancy, and those are by very definition extremely dangerous to the mother and treated as medical emergencies most of the time.

"It is the most common cause of death among women during the first trimester at approximately 6-13% of the total"

https://en.wikipedia.org/wiki/Ectopic_pregnancy

> where does it say it's often life threatening?

IUDs greatly reduce overall risk of pregnancy. The risk is not zero, though. When IUDs do fail, and they will, they increase the risk of ectopic pregnancies. The vast majority of those are located in the uterine tubes. Those are life threatening. There is no space for the fetus in the tube, it will rupture and cause severe bleeding which can and will kill the mother if left untreated. It's an important cause of acute abdomen.

Had it happen once with a partner (copper IUD, and it has been installed correctly), it was pretty terrible emotionally and physically.