Risk of sterility after contraception by IUD can be caused by IUD failure or by IUD complications. IUD failure includes expulsion, which is not always noted by the wearer, thus often leading to pregnancy. It is imperative to remove the device, when possible, to continue the pregnancy; this would avoid complications, risk of spontaneous abortion, and/or premature delivery. IUD failure can also cause ectopic pregnancy, in which case surgery is essential; unfortunately, 50% of women undergoing this type of surgery become infertile. IUD complications include uterine perforation and pelvic infection. Infections of any kind must be detected and treated as soon as possible to avoid salpingitis or pelviperitonitis, which both very often cause sterility. For these reasons the IUD should not be prescribed to nulliparous women who might desire children later in their life.