An IUD sits inside the uterine cavity with its top anchored at the fundus, the rounded uppermost portion of the uterus. Placement involves threading a slim inserter tube through the cervix and releasing the device so it unfolds at the top of the cavity, a process that typically takes only a few minutes. The details of where exactly it ends up, how it gets there, and what determines whether it stays put are more interesting than that summary suggests, because the uterus is not the simple pocket that diagrams make it look like.
The Target Location
The uterus is a hollow, muscular organ roughly the size and shape of an inverted pear. Its interior, the endometrial cavity, is lined with tissue that changes thickness throughout the menstrual cycle. The IUD’s ideal resting position is high in this cavity, at the fundus, because that is where the device can exert its contraceptive effects most evenly across the endometrium. When a copper IUD migrates away from the fundus, even partway down the endometrial canal, the risk of contraceptive failure rises.1PubMed. Migration of intrauterine devices: radiologic findings and implications for patient care Hormonal IUDs (the levonorgestrel-releasing type) are slightly more forgiving of imperfect position because the hormone they release acts locally on the surrounding tissue, so even one sitting a bit lower in the uterus may still provide adequate contraception.2PubMed. Management of Malpositioned Intrauterine Devices
Both types of IUD work in part by triggering a local inflammatory response inside the uterus. Copper IUDs release copper ions that are toxic to sperm, while levonorgestrel IUDs cause thinning and structural changes in the uterine lining on top of that foreign-body reaction.3PubMed. Copper-T intrauterine device and levonorgestrel intrauterine system: biological bases of their mechanism of action Both mechanisms depend on the device being inside the uterine cavity itself, not in the cervical canal or somewhere else it might drift.
Why One Size Does Not Fit All
Most IUDs sold today are T-shaped with a rigid or semi-rigid frame. The arms of the T spread out laterally to hold the device in place at the fundus, and a vertical stem runs downward through the cavity. The problem is that uterine cavities vary enormously from person to person. Ultrasound-based dimensional analyses have shown large variations in cavity size and shape, with the front-to-back diameter ranging from about 6 to 38 mm across different individuals.4PubMed Central. Dimensional analysis of the endometrial cavity: how many dimensions should the ideal intrauterine device or system have? A standard T-shaped device that fits perfectly in one uterus may be too wide for a narrow cavity or too small to sit snugly in a larger one. This mismatch is one reason researchers have explored frameless IUDs, which anchor to the fundal wall and hang freely as a thread of copper beads rather than trying to span the cavity with rigid arms.
In practice, the IUDs available in most countries come in only one or two sizes per brand, which means clinicians rely on proper placement technique and post-insertion checks rather than precise dimensional matching. Some newer hormonal IUDs have been designed with a slightly smaller frame for people with smaller uterine cavities, particularly those who have never been pregnant.
How the Insertion Works
The standard procedure begins with a bimanual exam where the clinician feels the size, shape, and angle of the uterus through the abdomen and vagina. A speculum is placed to visualize the cervix, and the cervix is usually cleaned with an antiseptic solution. Historically, the next step involves grasping the cervix with a tenaculum (a clamp-like instrument) to steady it, then passing a uterine sound, a thin rod, through the cervical canal to measure the depth of the cavity. The IUD, preloaded in its inserter tube, then follows the same path. Once the tip of the tube reaches the fundus, the clinician deploys the device, the T-arms spring open, and the tube is withdrawn. Thin threads attached to the base of the IUD trail through the cervix into the upper vagina, where they can later be checked.
Not every insertion follows that textbook sequence. A simplified approach tested in a clinical study skipped both the pelvic exam and the uterine sounding step, using ultrasound to confirm position afterward instead. About 80% of those insertions succeeded without any cervical manipulation at all, and the remaining 20% needed only a dilator to locate the cervical opening, not a full sounding.5PubMed. Assessment of a simplified insertion technique for intrauterine devices This matters because fewer instruments generally means less pain, and pain is the number-one concern people have about IUD insertion. Research into using the Valsalva maneuver (bearing down, as if straining) as a replacement for the tenaculum has also shown some promise as a way to reduce instrument use during the procedure.
During a cesarean section, an IUD can be placed directly into the uterus through the surgical incision after the placenta is delivered. In that scenario there is no need to pass anything through the cervix. One technique involves placing the device manually at the fundus; another uses the standard inserter tube through the incision and withdraws it, leaving the IUD behind.6PubMed Central. Conventional manual technique of post placental IUD insertion versus intra-cesarean post placental introducer withdrawal IUD insertion technique
What Insertion Actually Feels Like
Pain during IUD insertion gets talked about a lot online, and often in extremes: some people describe it as mild cramping, others as one of the most painful experiences of their lives. The research backs up both ends of that spectrum. For most people who have previously given birth, insertion causes moderate discomfort at most. For people who have never been pregnant (nulliparous), pain tends to be higher, and nulliparity is the single strongest predictor of insertion pain. That said, the majority of nulliparous people still report no more than moderate pain, and anticipated pain tends to be greater than the actual pain experienced. However, roughly 17% of nulliparous individuals and about 11% of those who have given birth report severe pain during the procedure.7Oxford Academic. Management of pain associated with the insertion of intrauterine contraceptives
Pain management options have improved. A paracervical block, an injection of local anesthetic around the cervix, significantly reduces pain at nearly every step of the insertion. In one randomized trial, people who received the block reported roughly 40% lower pain scores during placement compared to those who received no block.8PubMed Central. Paracervical Block for Intrauterine Device Placement Among Nulliparous Women: A Randomized Controlled Trial A systematic review and meta-analysis of multiple trials confirmed that paracervical blocks reduce pain during IUD placement, during tenaculum application, and during uterine sounding, and that overall patient satisfaction was higher when the block was used (about 80% satisfied versus 63% without the block).9Middle East Fertility Society Journal. Paracervical block for reducing pain during intrauterine device placement: a systematic review and meta-analysis of randomized controlled trials Topical lidocaine-prilocaine cream applied to the cervix before the procedure has also ranked well in network meta-analyses for reducing pain at tenaculum placement and during insertion itself.10PubMed. Evaluating different pain lowering medications during intrauterine device insertion: a systematic review and network meta-analysis
If you are considering an IUD and worried about pain, it is worth asking your provider specifically about a paracervical block or topical anesthetic. These options are underused in many settings despite solid evidence that they help. Some clinics also offer oral medications like ibuprofen beforehand or use smaller-gauge instruments, though the evidence for oral painkillers alone is weaker than for local anesthesia.
Checking That It Is in the Right Place
After insertion, the clinician typically trims the IUD threads to a length of a few centimeters so they hang just outside the cervix. You can check these strings yourself by reaching into the vagina with a clean finger and feeling for them at the cervix. The strings are the simplest ongoing indicator that the IUD has not moved. If they feel shorter, longer, or you cannot find them at all, it is worth getting the position checked by a provider.
The more definitive way to verify position is ultrasound. Clinicians use a standardized classification system to describe where exactly the IUD sits relative to the cervix and whether its arms are embedded in the uterine wall. The system assigns a letter based on the lowest point of the device (above the internal cervical opening, below it, entirely within the cervix, or fully expelled) and a number based on whether the arms extend into the muscular wall of the uterus on one or both sides.11PubMed. A proposed classification for intrauterine device position: the Tal-Reeves classification This classification helps providers make consistent decisions about whether a displaced IUD needs to be removed or can safely stay in place.
When the IUD Moves
Malposition is not rare. In one ultrasound-based study, about half of people with a malpositioned IUD had symptoms such as pelvic pain or abnormal bleeding, while nearly 47% were completely asymptomatic and discovered the problem only on imaging. Low placement within the uterine cavity was the most common pattern.12PubMed Central. Clinical Relevance and Symptom Patterns for Malpositioned Intrauterine Devices: A Retrospective Ultrasound-Based Study Certain uterine characteristics increase the odds of malposition. A retroflexed uterus (one that tilts backward rather than forward) was more common among people with malpositioned IUDs, as were structural abnormalities like fibroids projecting into the cavity. The presence of more fibroids and specifically submucosal fibroids was associated with higher malposition risk. Vaginal bleeding, pain, and missing strings at follow-up were the strongest clinical clues that something had shifted.13American Journal of Obstetrics and Gynecology. Uterine structural abnormality and intrauterine device malposition: analysis of ultrasonographic and demographic variables of 517 patients
Complete expulsion, where the IUD falls out entirely, is a different problem from internal displacement. Heavy menstrual bleeding is the strongest risk factor for expulsion. People with a diagnosis of heavy periods had an expulsion rate roughly three times higher than those without, and the difference was most pronounced in the first few months after insertion.14PubMed. Association between menorrhagia and risk of intrauterine device-related uterine perforation and device expulsion Younger age, higher body weight, and having had four or more pregnancies also raised the risk.15PubMed Central. Demographic, Reproductive, and Medical Risk Factors for Intrauterine Device Expulsion
Perforation and How Uncommon It Actually Is
Uterine perforation, where the IUD pushes through the wall of the uterus, is the complication that scares people the most, but it is also the least common. The overall incidence is roughly 1 in 1,000 insertions.16PubMed Central. Intrauterine devices and risk of uterine perforation: current perspectives A large study of over 326,000 IUD users found a cumulative incidence of about 0.2% at one year and 0.6% at five years. The risk was substantially higher for insertions done in the early postpartum period, especially between 4 days and 6 weeks after delivery, where the hazard was nearly 7 times that of non-postpartum insertions.17PubMed Central. Absolute Risks of Uterine Perforation and Expulsion Associated With Intrauterine Devices
Provider experience matters. Research has shown that less experienced healthcare providers and a lack of scheduled follow-up visits after insertion are independently associated with higher perforation risk. Getting an ultrasound both before and after insertion was more common among people who did not experience perforation, suggesting that imaging-guided care is protective.18PubMed Central. Risk factors of uterine perforation when using contraceptive intrauterine devices The reassuring takeaway is that perforation is uncommon in general and extremely uncommon when insertion is performed by an experienced clinician with appropriate follow-up.
Timing Around Pregnancy and Delivery
IUDs can be placed at various points relative to a pregnancy: immediately after vaginal delivery (within minutes of the placenta), in the early postpartum weeks, or later at a routine follow-up visit. Each window involves trade-offs. Immediate postplacental insertion has a high success rate and the advantage of convenience, since the patient is already in the delivery room, but the expulsion rate is considerably higher. One randomized trial found that 24% of IUDs placed immediately after vaginal delivery expelled within six months, compared to about 4% when placement was delayed to a later visit.19PubMed Central. Postplacental or Delayed Insertion of the Levonorgestrel Intrauterine Device After Vaginal Delivery A Randomized Controlled Trial Despite the higher expulsion rate, overall IUD use at six months was similar between the two groups because some people in the delayed group never returned for their insertion appointment.
A large observational study refined the picture further. The five-year cumulative expulsion incidence was highest for insertions within the first 3 days after delivery (about 11%) and lowest for insertions between 6 and 14 weeks postpartum (about 3%). Interestingly, breastfeeding was associated with a lower risk of expulsion, with breastfeeding individuals having about a 30% lower hazard compared to those not breastfeeding.20PubMed Central. Association of the Timing of Postpartum Intrauterine Device Insertion and Breastfeeding With Risks of Intrauterine Device Expulsion The sweet spot for postpartum placement appears to be waiting until the 6-to-14-week window, where expulsion risk drops to levels comparable with non-postpartum insertions, and the uterus has involuted enough to hold the device securely.
Does a Tilted Uterus Change Anything?
About 20-25% of people have a retroverted (tilted backward) uterus, which raises a natural question about whether IUD placement is trickier or less reliable in that anatomy. A large analysis of IUD insertion data found that insertion-related complications were rare regardless of uterine position, and that people with retroverted uteri did not have higher rates of accidental pregnancy, expulsion, or removal for bleeding and pain over 12 months of use.21PubMed. Do retroverted uteri adversely affect insertions and performance of IUDs? The caveat is that all insertions in that dataset were performed by experienced clinicians who presumably adjusted their technique to account for the angle. A retroflexed uterus was, however, more common among people with malpositioned IUDs in the imaging study mentioned earlier, so while the retroverted uterus itself does not disqualify you from IUD use, it may be a factor that an experienced inserter should be mindful of.13American Journal of Obstetrics and Gynecology. Uterine structural abnormality and intrauterine device malposition: analysis of ultrasonographic and demographic variables of 517 patients
Who Can Place an IUD
IUD insertion does not require a physician. Trained midwives and nurse practitioners perform insertions safely in many healthcare systems around the world. A study of certified midwives and obstetric nurse practitioners found no cases of uterine perforation, and 93% of patients reported satisfaction with the method.22PubMed Central. Outcomes of Intrauterine Device Insertion by Certified Midwives and Obstetric Nurse Practitioners In sub-Saharan Africa, trained study nurses achieved expulsion rates comparable to non-study providers and only modestly higher than study physicians, suggesting that the skill transfers well with proper training.23PubMed Central. Feasibility and Safety of IUD Insertion by Mid-Level Providers in Sub-Saharan Africa This is relevant if you live in an area where access to a gynecologist is limited; a well-trained mid-level provider can perform the procedure with equivalent safety. What matters more than the specific credential is adequate training and the availability of follow-up.
How IUD Design Got to Where It Is Now
The intrauterine device concept dates back nearly a century. The first widely recognized device was the Gräfenberg ring, introduced in 1928, which was a simple silver ring placed inside the uterus.24PubMed. Pioneers of the intrauterine device Decades of iteration followed, including various plastic loops and shields. The era of inert (non-medicated) IUDs effectively ended with the Dalkon Shield withdrawal in 1974 after it was linked to serious infections. That crisis set back IUD acceptance for years, but it also pushed the field toward the medicated devices used today. The copper T380A became the standard-bearer for copper IUDs, and it remains one of the most effective devices available.25PubMed. The IUD in evolution Levonorgestrel-releasing systems arrived later and now dominate the market in many countries. A frameless copper IUD, anchored directly into the fundal wall with a small knot rather than relying on a rigid frame, was developed in 1984 and is available in parts of Europe and elsewhere, though it never achieved widespread adoption in North America.
Design choices have practical consequences for fit and comfort. The rigid T-frame works well in an average-sized cavity but can cause pain or embed in the wall when the cavity is unusually narrow or oddly shaped. Smaller-frame hormonal IUDs have been introduced specifically for people with smaller uteri, and the frameless design sidesteps the size-mismatch problem entirely by not having a frame to mismatch. If you experience persistent cramping or pain after insertion, a size or design mismatch is one possibility worth discussing with your provider, alongside the more commonly considered causes like malposition.