Kyleena is a small, T-shaped intrauterine device (IUD) that prevents pregnancy by slowly releasing a low dose of a synthetic hormone called levonorgestrel directly into the uterus. It works primarily by thickening cervical mucus so sperm can’t reach an egg, and it’s approved to stay in place for up to five years.
The Three Ways Kyleena Prevents Pregnancy
Kyleena’s main job is changing the consistency of your cervical mucus. Normally, cervical mucus thins around ovulation to help sperm travel through the cervix. Levonorgestrel makes that mucus thick and sticky, creating a physical barrier that impairs or completely blocks sperm from reaching an egg. This is the primary way the device works.
The hormone also affects the lining of your uterus. It causes the endometrium to become thinner and less active, which reduces menstrual bleeding over time. While a thinner lining also makes it harder for a fertilized egg to implant, researchers note this effect hasn’t been directly demonstrated in living humans, so it’s considered secondary to the cervical mucus changes.
Some evidence suggests levonorgestrel can also partially suppress ovulation in some cycles, though this isn’t consistent enough to be considered a reliable part of how the device works. The combination of these effects makes Kyleena highly effective: fewer than 1 in 100 women become pregnant per year of use.
How Much Hormone It Releases
Kyleena contains 19.5 mg of levonorgestrel total, which is a smaller reservoir than some other hormonal IUDs. After insertion, it releases about 17.5 micrograms per day. That rate gradually declines over time, averaging about 9 micrograms per day across the full five years. For context, a daily birth control pill delivers 100 to 150 micrograms of levonorgestrel to your entire bloodstream, while Kyleena delivers its much smaller dose locally inside the uterus. This is why systemic side effects like mood changes or weight gain tend to be less common with hormonal IUDs than with pills, though they can still occur.
When It Starts Working
If Kyleena is inserted during the first seven days of your menstrual cycle, it’s effective immediately. If it’s placed at any other time in your cycle, you’ll need to use a backup method like condoms, or avoid vaginal intercourse, for seven days afterward. After that window, the hormone concentration in the cervical mucus is high enough to reliably block sperm.
What Happens to Your Period
Irregular bleeding and spotting are extremely common in the first three to six months after insertion. This is your body adjusting to the local hormone exposure, and it doesn’t mean anything is wrong. The pattern typically shifts toward lighter periods over time.
By the end of the first year, about 20% of Kyleena users stop getting a period entirely for stretches of 90 days or more. The progression is gradual: roughly 8% experience no bleeding by months four through six, climbing to about 14% by months seven through nine. Losing your period on Kyleena isn’t a sign of pregnancy or a health concern. It simply means the uterine lining has become thin enough that there’s nothing to shed. Your cycle returns to its previous pattern after removal.
Fertility After Removal
Kyleena doesn’t have a lasting effect on your ability to get pregnant. Once it’s removed, the cervical mucus returns to normal quickly, and the uterine lining rebuilds within one or two cycles. Studies consistently show that 70 to 75% of women who want to conceive after removal do so within 12 months. About 37% conceive within just the first three months. These numbers are comparable to what’s seen after stopping other forms of contraception, including non-hormonal copper IUDs.
One nuance worth knowing: some research suggests the rate of difficulty conceiving after IUD removal may be slightly higher than the general population average. But this finding is hard to separate from age-related fertility changes, since many people use an IUD for several years before trying to conceive.
Risks to Be Aware Of
Serious complications with Kyleena are uncommon but worth understanding. Pelvic inflammatory disease (PID), an infection of the uterus and fallopian tubes, occurred in 0.5% of women in clinical trials. The risk is highest in the first month after insertion, likely related to bacteria being introduced during the procedure rather than the device itself.
If you do become pregnant with Kyleena in place, which is rare, about half of those pregnancies are ectopic, meaning the embryo implants outside the uterus, usually in a fallopian tube. The overall rate of ectopic pregnancy in trials was approximately 0.2% per year. This doesn’t mean Kyleena causes ectopic pregnancies. It means the device is better at preventing normal uterine pregnancies than ectopic ones, so the rare pregnancies that do occur are disproportionately ectopic. If you miss a period and experience sharp pelvic pain or unusual bleeding, getting evaluated promptly matters.
Other possible issues include the device shifting out of position (partial or complete expulsion), which is most likely in the first few months, and perforation of the uterine wall during insertion, which is very rare. Checking for your IUD strings periodically helps you confirm the device is still in place.