The chances of getting pregnant with an IUD are extremely low, under 1% per year for both copper and hormonal types. IUDs are among the most effective contraceptives available, but no method is perfect. Over several years of use, a small number of pregnancies do occur, and understanding the specifics can help you know what to watch for.
How Effective Each Type of IUD Is
Hormonal and copper IUDs work differently, and their failure rates reflect that. Hormonal IUDs (brands like Mirena, Kyleena, Liletta, and Skyla) release a small amount of hormone that thickens cervical mucus, blocks sperm, and thins the uterine lining. These have a first-year failure rate of roughly 0.06%, based on a large European surveillance study. That translates to about 6 pregnancies per 10,000 users in a year.
Copper IUDs like ParaGard work by releasing copper ions that interfere with sperm movement and fertilization. They’re slightly less effective than hormonal IUDs but still highly reliable, with a first-year failure rate around 0.5% to 0.8%. A phase 3 trial of a low-dose copper IUD found a 1-year pregnancy rate of 1.26% and a cumulative 3-year rate of 2.47%. The standard copper T380A IUD tends to perform better than lower-dose versions.
For context, the birth control pill has a typical-use failure rate of about 7% per year, mostly because people miss doses. IUDs don’t require you to remember anything, which is a major reason their real-world effectiveness stays so close to their clinical-trial numbers.
How Risk Changes Over Time
One of the strongest advantages of IUDs is that their effectiveness holds steady, and in some cases improves, over years of use. Data from long-term studies of the copper T380A IUD showed zero pregnancies among women who kept the same device in place beyond 10 years, all the way through 15 and even 20 years of use. Women who are 35 or older at the time of insertion can use a copper IUD through menopause with a negligible risk of pregnancy.
Hormonal IUDs are currently approved for 3 to 8 years depending on the brand, and their effectiveness remains above 99% throughout their approved lifespan. Your risk of pregnancy doesn’t creep up midway through, as long as the device stays in place.
When an IUD Starts Working
The two types differ here. A copper IUD is effective immediately after insertion, no backup method needed. Hormonal IUDs are also immediately effective if placed within the first 7 days of your period. If a hormonal IUD is placed at any other point in your cycle, you need to use condoms or avoid intercourse for 7 days while the hormone builds up enough to block sperm.
What Raises the Risk of IUD Failure
The main reason IUDs fail is displacement or expulsion. If the device shifts out of position in your uterus, or falls out entirely, its protection drops significantly. General expulsion rates are relatively low, around 2% to 5% depending on the circumstances. The risk is higher if you’ve had an IUD placed shortly after a pregnancy loss or delivery, and it’s somewhat more common in the first few months after insertion.
Signs that your IUD may have moved include:
- IUD strings that feel shorter than usual, longer than usual, or uneven
- Unusually heavy bleeding
- Abnormal cramping that develops after you’ve already adjusted to the IUD
- Unusual vaginal discharge
- Not being able to feel the strings at all
Checking your strings monthly, especially in the first few months after insertion, is the simplest way to catch displacement early. If the strings feel different or you can’t find them, use a backup method and contact your provider for a check.
What Happens If You Do Get Pregnant
Pregnancies with an IUD in place carry a higher risk of being ectopic, meaning the embryo implants outside the uterus, usually in a fallopian tube. In the European surveillance study, 21 out of 118 IUD pregnancies were ectopic. That’s roughly 1 in 6, far higher than the ectopic rate in the general population (about 1 in 50 pregnancies). This doesn’t mean IUDs cause ectopic pregnancies. Because IUDs are so effective at preventing normal uterine pregnancies, the rare pregnancies that do occur are disproportionately ectopic.
An ectopic pregnancy is a medical emergency. If you have an IUD and experience a positive pregnancy test along with sharp pelvic pain, dizziness, or unusual bleeding, seek care promptly. Even without those warning signs, any confirmed pregnancy with an IUD in place needs medical evaluation to determine the location and whether the device should be removed. Early removal of the IUD, when possible, improves outcomes for pregnancies that are developing normally in the uterus.
Putting the Numbers in Perspective
Over a full year, roughly 2 to 8 out of every 1,000 copper IUD users will become pregnant. For hormonal IUD users, that number drops to about 1 to 2 per 1,000. Over five years, the cumulative risk for hormonal IUDs stays below 1%. These are some of the lowest failure rates of any reversible contraceptive, comparable to surgical sterilization.
The vast majority of IUD pregnancies happen because the device shifted or expelled without the user noticing. If your IUD is properly positioned and within its approved lifespan, the odds of pregnancy are vanishingly small.