Your body does not “reject” an IUD the way your immune system rejects an organ transplant, but the device can shift out of place, partially push itself out, or in rare cases perforate the uterine wall, all of which produce recognizable warning signs. The most common complication is expulsion, where the uterus pushes the device downward or out entirely, and it happens in roughly 2 to 10 percent of users depending on the type of IUD and when it was placed. Understanding what counts as a normal adjustment period versus a genuine complication can save you from both unnecessary worry and dangerous delays in getting care.
What People Mean by “Rejection” and What Actually Happens
When someone says their body is rejecting an IUD, they usually mean one of three things: the device is being expelled, the device has shifted to an abnormal position inside the uterus, or the device has partially or fully punctured through the uterine wall. These are distinct problems with different symptoms, different levels of urgency, and different treatments. Genuine allergic or immune reactions to IUD materials exist but are extraordinarily rare. One documented case involved a woman with a known copper allergy who developed widespread skin irritation within days of copper IUD placement, and the condition resolved after switching to a non-copper device.1PubMed Central. Intrauterine copper contraceptive devices and allergy to copper and nickel For the vast majority of people, the issue is mechanical, not immunological.
Expulsion and Its Warning Signs
Expulsion is the most common IUD complication. It means the uterus contracts or shifts in a way that pushes the device partially or completely out through the cervix. In a large retrospective study, copper IUD users experienced expulsion at about 10 percent over the study period, compared with roughly 5 percent for hormonal (levonorgestrel) IUD users.2PubMed Central. Continuation of copper and levonorgestrel intrauterine devices: a retrospective cohort study Expulsion can be partial, with the IUD sitting lower than it should but still inside you, or complete, meaning it falls out entirely.
The signs worth watching for include:
- Feeling the IUD itself: If you can feel hard plastic at or protruding from your cervix, or if the device falls out during a period or a bathroom visit, expulsion has occurred or is in progress.
- String length changes: Strings that feel significantly longer than usual can mean the device has moved downward. Strings that suddenly disappear may mean the device has shifted upward, been expelled without you noticing, or been drawn into the cervical canal.
- Cramping that restarts or worsens: Some cramping in the first weeks after insertion is expected. Cramping that returns after an initial settling period, or that intensifies rather than fading, can signal movement. One study found that women whose IUDs had shifted downward had measurably greater distances between the device tip and the uterine wall, which correlated with ongoing pelvic cramping at three months.3PubMed. Relationship between copper IUD complications and ultrasonographic findings
- Heavier or irregular bleeding: A change in bleeding pattern, especially if it happens after your body had already adjusted to the IUD, can point to displacement.
An IUD that has partially expelled no longer provides reliable contraception. If you suspect this has happened, use backup contraception and see your provider promptly.
Who Is More Likely to Experience Expulsion
Certain factors meaningfully raise the odds. A large study looking at demographic and reproductive risk factors found that heavy menstrual bleeding was the single strongest predictor of expulsion, especially when it had been diagnosed in both recent and past menstrual cycles. Younger age was also a substantial factor. Teens aged 14 to 19 had roughly two to three times the risk of expulsion compared with older users, with adjusted hazard ratios of about 2.3 for the hormonal IUD and 3.1 for the copper IUD in that age group.4PubMed Central. Association of Age and Parity With Intrauterine Device Expulsion Higher body weight and having had four or more previous pregnancies also increased risk.5PubMed Central. Demographic, Reproductive, and Medical Risk Factors for Intrauterine Device Expulsion
Timing of insertion matters as well, particularly after childbirth. A meta-analysis of postpartum IUD placement found that expulsion rates were dramatically higher when the device was placed immediately after delivery (about 10 percent) or in the early postpartum window before four weeks (about 30 percent), compared with less than 2 percent when placement was delayed until at least four weeks postpartum.6PubMed Central. Intrauterine Device Expulsion After Postpartum Placement: A Systematic Review and Meta-analysis If your IUD was placed shortly after you gave birth, the chances of it moving are considerably higher, and close follow-up in the first few months is particularly important.
Uterine anatomy plays a role, too. Fibroids or structural differences in the uterus can make it harder for the device to sit properly.7PubMed. CT imaging of intrauterine devices (IUD): expected findings, unexpected findings, and complications Women with a shorter uterine cavity have also been shown to experience more heavy bleeding with a copper IUD, likely because the device takes up proportionally more space.3PubMed. Relationship between copper IUD complications and ultrasonographic findings
Displacement and Embedment Without Full Expulsion
Sometimes the IUD does not come out but shifts to an abnormal position. It might rotate, tilt sideways, or slide lower in the uterine cavity. In more serious cases, the arms of a T-shaped device can embed into the muscular wall of the uterus. A study using three-dimensional ultrasound found that about 17 percent of patients evaluated had IUD arms abnormally located within the uterine muscle. Among those patients, 75 percent reported pain or abnormal bleeding, compared with about 35 percent of those whose devices were correctly positioned.8PubMed. Three-dimensional ultrasound detection of abnormally located intrauterine contraceptive devices which are a source of pelvic pain and abnormal bleeding
The tricky part is that malposition does not always cause symptoms. A retrospective study of 175 patients with malpositioned IUDs found that nearly half were asymptomatic, meaning the displacement was discovered incidentally during an ultrasound done for another reason.9PubMed Central. Clinical Relevance and Symptom Patterns for Malpositioned Intrauterine Devices: A Retrospective Ultrasound-Based Study When symptoms do appear, pelvic pain and abnormal bleeding are the most common complaints. That same study noted that low placement within the uterus was the most frequent type of malposition. Ultrasound is the first-line tool for checking device position when something feels off.10PubMed Central. Ultrasonography of intrauterine devices
For asymptomatic malposition discovered by chance, the decision about whether to remove or replace the IUD is individualized. Guidelines suggest particular caution in younger people and anyone who has expelled an IUD before, since those groups face higher odds of progression to full expulsion.
Perforation Is Rare but Serious
Uterine perforation, where the device punctures through the wall of the uterus into the abdominal cavity, is the most alarming IUD complication but also the least common. The estimated incidence is about one in every 1,000 insertions.11PubMed Central. Intrauterine devices and risk of uterine perforation: current perspectives In very rare cases, a perforated device can migrate into surrounding structures such as the bowel or bladder.
Perforation can happen at the time of insertion or develop gradually afterward. Warning signs include sudden sharp pain during or after insertion that does not improve, persistent pelvic or abdominal pain in the weeks that follow, and strings that become impossible to find. A study comparing patients with and without perforation found that abdominal pain was the most frequent complaint among those whose IUDs had perforated. The same study identified less experienced providers and the absence of follow-up ultrasound as factors that made perforation more likely to go undetected.12PubMed Central. Risk factors of uterine perforation when using contraceptive intrauterine devices Some research also shows a possible link between breastfeeding at the time of insertion and perforation risk, though no causal relationship has been confirmed.11PubMed Central. Intrauterine devices and risk of uterine perforation: current perspectives
If perforation is suspected, imaging with ultrasound or CT will confirm where the device ended up. A fully embedded IUD that remains inside the uterine wall may be removed with hysteroscopy, a minimally invasive camera-guided procedure. When the device has migrated partially or fully through the wall into the abdominal cavity, laparoscopic or even open surgery may be necessary.13Annals of Case Reports. Fully Embedded IUD: Hysteroscopic Management Using X-ray
Infection and the IUD
People often worry that an IUD causes pelvic inflammatory disease (PID). The reality is more nuanced. The risk of infection is modestly elevated in the first few weeks after insertion, largely because the insertion procedure can introduce bacteria from the cervix into the uterus. In one study of IUD users who developed PID, about a quarter had their IUD placed less than four weeks before the diagnosis.14PubMed. Pelvic inflammatory disease among users and non-users of an intrauterine device After that initial window, the IUD itself does not meaningfully increase your ongoing risk for pelvic infection. A prospective study following hormonal IUD users over two years found that only about 0.5 percent were diagnosed with a pelvic infection, and all of them had tested negative for chlamydia around the time of placement.15PubMed. A prospective assessment of pelvic infection risk following same-day sexually transmitted infection testing and levonorgestrel intrauterine system placement
Signs of infection include fever, worsening pelvic pain, foul-smelling discharge, and pain during sex. If you develop these symptoms, seek care promptly. PID with an IUD in place can often be treated with antibiotics without removing the device, but your provider will make that call based on how severe the infection is.
Why String Checks Are Not as Reliable as You Might Think
Standard advice after IUD placement is to check your strings periodically by reaching into the vagina and feeling for the thin threads hanging from the cervix. If the strings feel the same length and you can locate them, the IUD is probably in place. If they feel longer, shorter, or are missing, something may have changed. The logic is sound in theory, but the evidence suggests string checks have significant limitations as a self-screening tool.
A study of postplacental copper IUDs found that a string check had only about 36 percent sensitivity for detecting a malpositioned device. In other words, most incorrectly positioned IUDs were missed by string checks alone. The specificity was better at about 85 percent, meaning that if you can find your strings and they feel normal, that is somewhat reassuring but far from a guarantee.16PubMed Central. Six-month expulsion of postplacental copper intrauterine devices placed after vaginal delivery A separate retrospective study confirmed that being able to see the strings during a clinical exam did not reliably rule out malposition.9PubMed Central. Clinical Relevance and Symptom Patterns for Malpositioned Intrauterine Devices: A Retrospective Ultrasound-Based Study
When strings are not visible, the cause is often something benign. Strings can curl up into the cervical canal, or cervical mucus changes can make them harder to feel. But invisible strings can also signal expulsion, perforation, or pregnancy, so if you cannot find yours, a clinical evaluation with ultrasound is warranted.17PubMed Central. In-office retrieval of intrauterine contraceptive devices with missing strings Your provider will typically start with a gentle attempt to locate the strings using a small brush or retrieval tool, followed by an ultrasound to confirm where the device actually sits.
Menstrual Cups and IUD Displacement
This is a practical concern that has gained attention in recent years as menstrual cup use has become more popular. The worry is that the suction created by removing a cup could tug on IUD strings or physically dislodge the device. The evidence increasingly supports that worry, at least for certain IUD types.
A randomized trial comparing copper IUD users who did and did not use menstrual cups found that cup users had roughly three times the rate of expulsion over 12 months (about 16 percent versus 5 percent). The effect was most pronounced with a smaller copper IUD design, where cup users had over three times the adjusted odds of expulsion over 36 months. Accidental self-removal, where women pulled the IUD out along with the cup, accounted for a meaningful portion of these events.18PubMed Central. Menstrual cup use and intrauterine device expulsion in a copper intrauterine device randomized trial A case-control study found a similar pattern: menstrual cup use was reported by about 41 percent of patients with a displaced IUD compared with only 17 percent of those with a well-positioned device, yielding about three times the adjusted odds of displacement.19PubMed Central. The use of a menstrual cup as a risk factor for displacement of intrauterine devices: a case-control study
If you use both a menstrual cup and an IUD, the practical advice is to break the seal of the cup thoroughly before pulling it out, avoid tugging on the cup if you feel resistance, and check that your IUD strings are not caught in the cup after removal. Some providers recommend menstrual discs as a lower-risk alternative, since discs sit higher in the vaginal canal and do not rely on the same suction mechanism, though head-to-head data comparing discs and cups in this context is limited.
Pregnancy With an IUD in Place
IUDs are among the most effective contraceptive methods, but no method is perfect. When pregnancy does occur with an IUD in place, one concern is ectopic pregnancy, where the embryo implants outside the uterus, most often in a fallopian tube. A large study found that ectopic pregnancy rates varied by IUD type. The highest-dose hormonal IUD (52 mg levonorgestrel) had the lowest ectopic rate, at about 0.04 per 100 person-years, while the lowest-dose hormonal IUD (13.5 mg) had the highest, at about 0.18 per 100 person-years. Copper IUD users fell in between, at about 0.07 per 100 person-years.20NEJM Evidence. Intrauterine Devices and Risk of Ectopic Pregnancy
The overall rates are still very low, but they mean that if you have an IUD and miss a period, experience one-sided pelvic pain, or have unexpected vaginal bleeding alongside a positive pregnancy test, you should be evaluated urgently. Ectopic pregnancy is a medical emergency that requires immediate treatment.
What Happens If You Expel One IUD and Want Another
Experiencing one expulsion does not automatically mean you cannot use an IUD again, but the odds of a repeat event are meaningfully higher. In a study tracking women who had a copper IUD re-inserted after expulsion, the cumulative expulsion rate with the replacement device was about 22 percent at six months and about 31 percent by the end of the first year. Women who expelled their first IUD within the first three months had an especially high rate of expelling the second one.21PubMed. Performance of copper intrauterine devices when inserted after an expulsion
If you want to try again after an expulsion, your provider should discuss these odds with you. Switching to a different IUD size or type sometimes helps, particularly if the first device was poorly matched to your uterine dimensions. Some people try a second time and have no further issues. Others ultimately move to a different contraceptive method. Factors like your age, whether you have heavy periods, and how quickly the first expulsion happened all feed into that decision.
Normal Side Effects Versus Red Flags
In the first one to three months after insertion, cramping, spotting, and heavier periods (especially with the copper IUD) are expected. These side effects usually diminish as the uterus adjusts to the device. The hormonal IUD can cause irregular spotting for several months before bleeding tapers off, sometimes to nothing. These patterns are annoying but not dangerous.
The line between a normal adjustment and something worth investigating is not always obvious, but a few signals should prompt a visit to your provider:
- Pain that worsens over time: Cramping that fades gradually is normal. Pain that escalates, becomes sharp on one side, or develops weeks after initial discomfort had subsided is not.
- Fever or unusual discharge: These point toward infection, especially if they appear in the first month after insertion.
- Missing or dramatically changed strings: As noted above, this warrants an ultrasound, even though the cause is usually benign.
- A positive pregnancy test: Any pregnancy with an IUD in place needs immediate evaluation to rule out ectopic implantation and to decide whether the IUD should be removed.
- Feeling the device outside your cervix: This confirms expulsion is happening and you should stop relying on the IUD for contraception.
If you are unsure, err on the side of calling your provider. An ultrasound is quick, painless, and gives a definitive answer about where the IUD sits. The cost of an unnecessary appointment is low compared to the cost of missing a perforation or ectopic pregnancy.
The Role of Follow-Up Ultrasound
Not all clinics routinely schedule a follow-up ultrasound after IUD placement, but the evidence suggests it can catch problems early. The study on perforation risk factors found that patients who had an ultrasound performed both before and after IUD insertion were significantly less likely to end up with an undetected perforation.12PubMed Central. Risk factors of uterine perforation when using contraceptive intrauterine devices And because string checks alone are unreliable at detecting malposition, an imaging-based confirmation adds a layer of certainty that a physical check cannot provide.
Some providers schedule a routine check at four to six weeks after insertion. If yours does not, you can ask for one, especially if you fall into a higher-risk category: younger age, postpartum placement, history of heavy periods, or a prior expulsion. If everything looks good on that first follow-up, you can feel more confident going forward. Problems that have not appeared by three to six months are much less likely to arise later, though they are not impossible. Late complications like gradual embedment or delayed perforation do occur and can surface months or even years after insertion, so persistent or new-onset symptoms at any point warrant evaluation.