For experienced medical practitioners, the risk of perforation is one per 1,000 insertions or less. With postpartum insertions, perforation of the uterus is more likely to occur when uterine involution is incomplete; involution usually completes by 4–6 weeks postpartum. Special considerations apply to women who plan to breastfeed. If perforation does occur it can damage the internal organs, and in some cases surgery is needed to remove the IUD. Pregnancy complications: Although the risk of pregnancy with an IUD is very small, if one does occur there is an increased risk of serious problems. These include ectopic pregnancy, infection, miscarriage, and early labor and delivery. As many as half the pregnancies that occur in Mirena users may be ectopic. The incidence rate of ectopic pregnancies is approximately one per 1000 users per year. Immediate removal of the IUD is recommended in the case of pregnancy. No pattern of birth defects was found in the 35 babies for whom birth outcomes were available at the time of FDA approval. Infection: The insertion of the IUD does have a small risk of pelvic inflammatory disease (PID). Concurrent infection with gonorrhea or chlamydia at the time of insertion increases the risk of pelvic inflammatory disease. If PID does occur, it will most likely happen within 21 days of insertion. The device itself does not increase the risk of infection.
In addition to birth control, the hormonal IUD is used for prevention and treatment of:

Heavy menstrual periods
Endometriosis and chronic pelvic pain
Adenomyosis and dysmenorrhea
Anemia
Endometrial hyperplasia (especially in pre-menopausal women who wish to maintain fertility in the treatment of endometrial hyperplasia)
In some cases, use of a hormonal IUD may prevent a need for a hysterectomy.Advantages:

Considered one of the most effective forms of reversible birth control
Can be used while breastfeeding (see also nursing mothers)
No preparations needed before sex, though routine checking of the device strings by patient and physician is advised to ensure proper placement remains intact
90% of users who wish to become pregnant do so within 24 months of removal. May experience lighter periods (some women stop having periods completely, see also amenorrhea)
Effective for up to three to seven years (depending on the IUD)Disadvantages:

Irregular periods and spotting between periods often occurs after insertion This usually improves after three to six months. Moderate to severe discomfort may be experienced during insertion procedure, including uterine cramping and back pain. Other potential adverse effects and risks

Effectiveness
After insertion, Mirena is effective at preventing pregnancy for up to seven years. Kyleena is approved for five years and Skyla is approved for three years.The hormonal IUD is a long-acting reversible contraceptive, and is considered one of the most effective forms of birth control. The first year failure rate for the hormonal IUD is 0.1-0.2% and the five-year failure rate is 0.7-0.9%. These rates are comparable to tubal sterilization, but unlike sterilization the effects of the hormonal IUD are reversible.