How does an IUD work? Can it be used for emergency contraception?

Dear Alice,

On the Planned Parenthood website, it indicates that the copper IUD can be used as emergency contraception if inserted within 5 days of unprotected sex, and that it is 99.9 percent effective as emergency contraception. I had never heard this before. The website also says that the IUD works by affecting the way that sperm move, and that there is no evidence that it works by preventing an embryo from implanting in the uterus. What if the egg meets the sperm in those five days?

Another IUD question. I understand that IUDs are associated with a small increase in risk of pelvic inflammatory disease (PID), which can lead to infertility. I've heard you can have PID which goes symptom-free and undetected. What can a woman do to make sure she doesn't have PID after getting an IUD?


Dear Reader, 

Contraceptive technology can certainly be complicated, but it doesn’t have to be. What you've read is correct. The copper intrauterine device (IUD) can be used as emergency contraceptive (EC) to prevent pregnancy for up to five days after unprotected sex, and it’s actually the most effective method out there right now. Essentially, the copper in the IUD helps impedes the sperm so they can’t reach and fertilize the egg. It may also change the lining of the uterus to prevent a fertilized egg from attaching to the uterus wall. So even if the two were to meet, the likelihood of it implanting would be greatly reduced. Whatever the mechanism, it sure is effective! Read on to learn more. 

To understand how a copper IUD works as EC, a little background info is needed. One part of reproductive health that many don’t realize is that conception (when sperm meets an egg) doesn’t have to happen immediately after sex. Sperm actually live inside the uterus and fallopian tubes for up to several days, just hanging around and waiting for an egg to show up. Pregnancy only occurs if an egg is released during that window of time, the sperm and egg successfully combine, and the fertilized egg then successfully implants in the uterine lining. That’s a lot of steps! All in all, the process of becoming pregnant doesn't happen overnight and interfering with any one of the steps prevents a pregnancy, which is precisely where emergency contraception comes into play. 

On to the copper IUD: The device is a T-shaped piece of plastic that has copper piping along the "T." It's inserted through the cervix and sits in the uterus to prevent pregnancy. Copper IUDs trigger anatomical and biochemical changes in the uterus, producing a toxic environment for incoming sperm and preventing them from traveling into the fallopian tubes and fertilizing an egg. No working sperm means no pregnancy, regardless of whether the body has already released an egg or not. This makes the copper IUD different from other types of EC, which are typically hormonal and prevent pregnancy primarily by preventing the body from releasing an egg. In the case of an already released egg, it may also prevent fertilization of an egg and stop it from implanting into the uterus wall.  

So how does an IUD relate to pelvic inflammatory disease (PID)? An early version of an IUD from the 1970s, the Dalkon Shield, did cause PID in some users. However, that version wasn’t subject to all of the rigorous safety testing that today’s devices are. Today’s IUDs have been extensively studied, and researchers have found no association between IUDs and PID. The real culprit of PID? Sexually transmitted infections (STIs). If a person has an infection, such as chlamydia or gonorrhea, when they have an IUD inserted, the risk for PID is increased. However, for those without any infections, the risk of PID isn’t related to IUD use. A health care provider will test for STIs before inserting an IUD to avoid any chance of a PID infection. It’s critical to note that while an IUD does protect against pregnancy, it’s doesn’t protect against STIs. If you want to ensure STI protection as well, using a barrier method such as condoms can help to reduce the risk of STI transmission.  

If you’re considering a copper IUD, whether as a form of emergency contraception or otherwise, it involves a visit to your health care provider. This can be helpful to keep in mind in a time-sensitive situation depending on the availability of your providers on short notice. It's also a method that can be used as a long-term birth control method (up to ten to twelve years) — but if that's not what you're looking for, it's wise to consider other options. The good news is that there are other methods of EC in the form of a low-risk and effective hormonal pill. Most one-pill formulations of EC include the hormone levonorgestrel and are available for sale on the retail shelves at many pharmacies and drugstores. For these formulations, no prescription is needed, and proof-of-age isn’t required to purchase. They're most effective if taken up to 72 hours after sex. Another type of EC that comes in a pill form, ulipristal acetate (the only available brand in the US is called Ella) is effective up to 120 hours after sex — but it requires a prescription. Interested in learning more about these methods? Try browsing some of the Q&As about emergency contraception in the Go Ask Alice! Sexual and Reproductive Health archives. You could also learn more by meeting with a health care provider or health promotion specialist, who could talk through these and other forms of birth control with you. 

Whichever route you choose, know that all forms of emergency contraception are more effective the sooner they are used. 

Take care, 

Last updated Aug 13, 2021
Originally published Aug 14, 2009

Submit a new comment


This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

The answer you entered for the CAPTCHA was not correct.