Implantation of a levonorgestrel-releasing IUS results in high levels of the hormone in the endometrium, causing thickening of the cervical mucus and making it impenetrable to sperm.
Differing release rates
Kyleena releases an average of 9 micrograms levonorgestrel per 24 hours over five years. This compares with an average of 6 micrograms levonorgestrel per 24 hours over three years for Jaydess and 15.6 micrograms levonorgestrel per 24 hours over three years for Levosert. Mirena releases 20 micrograms levonorgestrel per 24 hours initially, reducing to 10 micrograms per 24 hours five years after insertion.
Research has shown that the impact of lower-dose IUSs (eg, Kyleena, Jaydess) on cervical function is similar to that of higher-dose systems (eg, Levosert, Mirena).
Efficacy demonstrated in trials
The efficacy of Kyleena was assessed in a five-year clinical trial involving 1,452 women aged 18 to 35 years, almost 40 per cent of whom were nulliparous.
Over the five years (57,313 cycles) a total of 13 pregnancies occurred, giving a cumulative five-year Pearl Index of 0.29 (95% CI 0.16-0.50) and a five-year cumulative failure rate of 1.44 per cent. The efficacy over five years was not affected by parity or age.
Self-reporting by women in the study showed that bleeding patterns improved greatly over time, as did rates of dysmenorrhoea. Return of fertility after removal of Kyleena was also demonstrated, with 71.2 per cent of women who discontinued use of the device in order to become pregnant conceiving within 12 months.
Benefits versus other IUSs
Kyleena offers longer contraceptive protection that the other low-dose levonorgestrel IUS available in the UK (five years vs three years for Jaydess). In addition, it has a smaller frame (30mm high x 28mm wide) and a narrower applicator than the original high-dose device (Mirena) potentially allowing less painful placement, and a lower incidence of amenorrhoea compared with high-dose devices.