The intrauterine device (IUD) represents a highly effective method of long-acting reversible contraception (LARC). An IUD is a small, T-shaped device inserted into the uterus by a healthcare provider, and it can remain effective for several years. There are two primary types: the hormonal IUD, which releases a low dose of progestin hormone, and the copper IUD, which is entirely hormone-free. The central question for many users is what “unprotected sex” means when this device is in place, especially since the IUD provides robust protection against pregnancy but none against sexually transmitted infections (STIs).
IUD Effectiveness as Contraception
The IUD is one of the most reliable forms of reversible birth control available, with efficacy rates exceeding 99% in preventing pregnancy. The IUD’s success is largely due to its mechanism of action and the fact that user error is essentially eliminated once the device is correctly inserted.
The two types of IUDs prevent conception through distinct biological pathways. Hormonal IUDs work primarily by releasing a progestin hormone that thickens the cervical mucus, creating a physical barrier that prevents sperm from reaching an egg. This hormone also thins the uterine lining and, in some cases, may suppress ovulation.
The copper IUD, conversely, works through a non-hormonal mechanism by continuously releasing copper ions into the uterine environment. These copper ions are toxic to sperm, impairing their motility and viability, which prevents fertilization. Both devices also create a localized inflammatory reaction within the uterus, which makes the environment inhospitable for sperm.
Does the IUD Protect Against STIs?
Despite the IUD’s high effectiveness against pregnancy, it provides no protection against sexually transmitted infections (STIs). The IUD is placed inside the uterus and does not create a physical barrier to block the exchange of bodily fluids or skin-to-skin contact. Therefore, having an IUD does not change the medical definition of “unprotected sex” when the risk of disease is considered.
Unprotected sex is defined by the potential for disease transmission, not solely by the risk of conception. STIs, including HIV, Chlamydia, Gonorrhea, and Human Papillomavirus (HPV), are transmitted through contact with infected skin, mucous membranes, or bodily fluids.
The lack of protection means that a person with an IUD is fully protected from pregnancy but remains completely vulnerable to any STI exposure. Relying on an IUD alone means accepting a full risk of contracting an STI if a partner is infected.
When Barrier Methods Are Essential
Barrier methods, such as external (male) or internal (female) condoms, remain the only form of contraception that protects against STIs. Even with the IUD in place, condoms are necessary to protect sexual health. This is particularly true when an individual has a new sexual partner, or if either partner has multiple concurrent partners.
The decision to forgo barrier methods should only be made after mutual communication and verified STI testing. Both partners should discuss their sexual history and agree to be tested for a full panel of STIs, including those that are often asymptomatic like Chlamydia and Gonorrhea. Experts recommend that individuals in a sexually active, non-monogamous relationship or who have a partner whose status is unknown should use condoms every time.
For couples entering a mutually monogamous relationship, the use of condoms can be discontinued only after both partners have received recent negative STI test results. Regular re-testing, often annually, is still recommended for all sexually active individuals, regardless of relationship status, as a routine part of sexual healthcare.
Assessing the Risk of Pelvic Inflammatory Disease
Pelvic Inflammatory Disease (PID) is a health concern linked to STI exposure in IUD users. PID is an infection of the reproductive organs, including the uterus, fallopian tubes, and ovaries, and it is most often caused by untreated STIs, particularly Chlamydia and Gonorrhea. The presence of the IUD does not cause PID, but it can provide a pathway for existing bacteria to reach the upper reproductive tract.
The risk of PID is highest in the first 20 days following IUD insertion, primarily because the insertion procedure can introduce pre-existing bacteria from the cervix into the uterus. After this initial period, the overall risk of PID among IUD users is low. The greatest ongoing risk factor for PID remains exposure to an STI through unprotected sex.
Symptoms of PID can be subtle or severe, and may include:
- Lower abdominal or pelvic pain.
- Unusual or foul-smelling vaginal discharge.
- Fever or chills.
Any person with an IUD experiencing these symptoms should seek immediate medical attention, as prompt treatment with antibiotics is necessary to prevent long-term complications. Untreated PID can lead to chronic pelvic pain, ectopic pregnancy, and infertility.