Efficacy and safety with Mirena
Efficacy is usually mentioned as the single most important reason for choosing a contraceptive1. So, it is important to make sure that women are aware that Mirena provides very effective protection against pregnancy for up to five years. They can be advised that large-scale trials have shown that the risk of pregnancy is around 0.2% after the first year of use and cumulatively 0.7% after five years of use.
Table 6: Comparison of unintended pregnancies with different contraceptive methods2.
|Method||% of unintended pregnancies within first year of use|
|Typical use||Perfect use|
Women also want reassurance that Mirena is safe to use, and they can be informed that many large studies have assessed the safety of Mirena. These studies have shown that:
- women do not gain more weight while using the IUS more than those using a non-hormonal method of contraception (Cu-IUD). (5-year study)
- the rate of pelvic inflammatory disease is lower with use of Mirena, compared to the Cu-IUD3
- there is a low incidence of ectopic pregnancy with Mirena use3 which has also been shown to be of a lower incidence than in women using no contraception at all4. The ectopic pregnancy rate with Mirena is approximately 0.1% per year compared to women not using any contraception (0.3% - 0.5% per year)5
- the good safety profile of Mirena is maintained during long-term use6
- while uterine perforations with use of Mirena are rare, the risk of perforations may be increased in post-partum placements in lactating women, and in women with a fixed retroverted uterus5. The incidence of uterine perforation during placement is less than 1 per 1000 placements5 and appears to be similar to that observed with CU-IUDs7. If perforation or penetration occurs, it may decrease the effectiveness of Mirena, and it must be removed5
- occurrence of cervical dysplasia is not increased in women using Mirena8
- use of Mirena is not associated with an increased risk of development of breast cancer9,10
- difficulties with the placement of Mirena may occur in some women, especially nulliparous and post-menopausal women. In a clinical study of nulliparous women, Suhonen et al.11 reported a difficult placement in 15% of cases. 13% of cases required paracervical blockade and/or dilatation. Pain at placement was reported as severe in 21% of nulliparous women and in 3.6% in parous women
- pre-clinical safety studies showed no special hazard for humans based on studies of safety pharmacology, toxicity, genotoxicity, and carcinogenic potential of levonorgestrel. The safety evaluations of the different components of Mirena have not revealed bio-incompatibility5