Pregnancy also has "a lot" of negative impacts. Quoting from http://www.plannedparenthood.org/learn/birth-control/iud http://www.plannedparenthood.org/learn/bi

Pregnancy also has "a lot" of negative impacts. Quoting from http://www.plannedparenthood.org/learn/birth-control/iud http://www.plannedparenthood.org/learn/birth-control/iud in the section about disadvantages: > You may have: - mild to moderate pain when the IUD is put in - cramping or backache for a few days - spotting between periods in the first 3–6 months - irregular periods in the first 3–6 months — with Mirena or Skyla - heavier periods and worse menstrual cramps — with ParaGard > Pain relievers can usually reduce bleeding, cramping, and other discomforts. If they are severe and do not seem to lessen, tell your health care provider. > Serious problems with the IUD are rare. ... In rare situations, a woman could develop an infection when using the IUD. This happens if bacteria get into the uterus when the IUD is inserted.