IUDs are one of the most effective forms of birth control available. Fewer than 1 in 100 IUD users become pregnant in the first year with typical use, putting IUDs in the same top tier as the implant. Across a 43-country analysis, IUDs had a 12-month typical-use failure rate of 1.4 per 100 users, compared to 5.5 for the pill and 5.4 for male condoms.
How IUDs Compare to Other Methods
The CDC groups contraceptive methods into tiers based on real-world effectiveness, and IUDs sit at the top alongside implants. The reason is simple: once an IUD is placed, there’s nothing to remember, refill, or use correctly in the moment. That eliminates the most common source of failure with other methods.
Here’s how 12-month typical-use failure rates stack up across methods:
- Implant: 0.6 pregnancies per 100 users
- IUD: 1.4 per 100 users
- Injectable: 1.7 per 100 users
- Pill: 5.5 per 100 users
- Male condom: 5.4 per 100 users
- Withdrawal: 13.4 per 100 users
- Periodic abstinence (rhythm method): 13.9 per 100 users
The small gap between IUDs and implants largely comes down to the possibility of expulsion, where the IUD partially or fully slips out of position. When the device stays in place, the failure rate is extremely low.
Hormonal vs. Copper: How Each Type Works
Both types of IUD create a hostile environment for sperm, but they do it differently. The copper IUD (ParaGard) releases copper ions that are directly toxic to sperm, impairing their ability to move and survive. It also triggers a local inflammatory response in the uterus that further prevents fertilization. No hormones are involved.
Hormonal IUDs release a small, steady dose of a progestin called levonorgestrel directly into the uterus. This thickens cervical mucus so sperm can’t easily pass through, thins the uterine lining, and weakens sperm function. The hormone stays largely local, meaning blood levels are much lower than with the pill or other systemic methods.
Both types are highly effective. The practical differences come down to side effects, how long they last, and whether you want hormones involved.
Available IUDs and How Long They Last
Five IUDs are currently available in the U.S., each with a different approved lifespan and hormone dose:
- ParaGard (copper): No hormones. Approved for 10 years.
- Mirena: 52 mg levonorgestrel, releasing about 20 mcg per day initially. Now FDA-approved for 8 years.
- Liletta: 52 mg levonorgestrel, releasing about 18.6 mcg per day initially. Approved for 5 years.
- Kyleena: 19.5 mg levonorgestrel, releasing about 17.5 mcg per day initially. Approved for 5 years.
- Skyla: 13.5 mg levonorgestrel, the lowest dose. Approved for 3 years.
Mirena’s extended approval to 8 years came after a U.S. study followed 362 women into their sixth through eighth years of use. Only two pregnancies occurred during those extra three years, yielding a cumulative failure rate of 0.68%. Its effectiveness in years 6 through 8 was essentially the same as during the original five-year window.
When Protection Starts
The copper IUD begins working immediately after insertion, regardless of where you are in your menstrual cycle. This is because its contraceptive effect comes from the copper itself, not from any hormonal changes that need time to develop.
Hormonal IUDs work a bit differently. If placed within seven days of the start of your period, protection begins right away. If placed at any other point in your cycle, you’ll need to use backup contraception (like condoms) for seven days while the hormones take effect on your cervical mucus.
The Copper IUD as Emergency Contraception
The copper IUD doubles as the most effective form of emergency contraception when inserted within five days of unprotected sex. It’s roughly 10 times more effective at preventing pregnancy than emergency contraceptive pills, according to research from the National Institute of Child Health and Human Development. A recent study also found that the levonorgestrel (hormonal) IUD performed comparably to the copper IUD for emergency use, with the added benefit of less discomfort during placement.
Unlike emergency contraceptive pills, which are a one-time intervention, an IUD placed for emergency purposes then stays and provides ongoing contraception for years.
What Can Reduce Effectiveness
The main thing that can undermine an IUD’s effectiveness is expulsion. This means the device shifts out of its correct position in the uterus, sometimes partially and sometimes completely. A large cohort study found an overall expulsion rate of about 15 per 1,000 person-years. Roughly half of all expulsions happen in the first year, with the cumulative rate at five years being about double the one-year rate.
Several factors increase expulsion risk. People with heavy menstrual bleeding have the highest risk, followed by those with a higher BMI, younger age at insertion, or four or more previous births. That said, expulsion remains uncommon overall, and these risk factors don’t make IUDs a poor choice for those groups.
You can check that your IUD is still in place by feeling for the strings that hang through the cervix. If the strings feel longer or shorter than usual, or if you can feel hard plastic, the device may have moved. A quick ultrasound can confirm proper placement.
Ectopic Pregnancy Risk
IUDs dramatically reduce the overall risk of any pregnancy, including ectopic pregnancies (where a fertilized egg implants outside the uterus, usually in a fallopian tube). But in the rare event that pregnancy does occur with an IUD in place, the chance of it being ectopic is higher than it would be with a natural conception.
A large study published in NEJM Evidence found that ectopic pregnancy rates varied by IUD type. The highest-dose hormonal IUD (52 mg, like Mirena) had the lowest ectopic pregnancy rate at 0.04 per 100 person-years. The copper IUD came in at 0.07, and the smallest hormonal IUD (13.5 mg, like Skyla) had the highest rate at 0.18 per 100 person-years. All of these numbers are very small in absolute terms, but they’re worth being aware of. Persistent lower abdominal pain, vaginal bleeding, or dizziness after a missed period warrants prompt evaluation.
How Long Effectiveness Lasts
Unlike pills or condoms, where effectiveness resets with every use, an IUD’s protection is continuous and doesn’t degrade meaningfully over its approved lifespan. The hormonal dose does decline gradually (Mirena’s daily release drops from about 20 mcg to 10 mcg over its lifespan, for example), but the contraceptive effect remains strong throughout the approved duration.
Fertility returns quickly after removal. Most people can become pregnant within one to two cycles, since IUDs don’t suppress ovulation the way some other hormonal methods do. There is no delay in fertility associated with how long the IUD was in place.