IUI, or intrauterine insemination, is a fertility treatment where washed and concentrated sperm are placed directly into the uterus during ovulation. It’s one of the simplest and least expensive assisted reproduction options, with per-cycle success rates ranging from about 2% to 20% depending on age. The goal is to shorten the distance sperm need to travel, giving them a better chance of reaching and fertilizing an egg in the fallopian tube.
How IUI Works
In natural conception, sperm must travel from the vagina through the cervix, into the uterus, and up into the fallopian tubes to meet an egg. That’s a long journey, and many sperm don’t survive it. IUI skips the first part of that trip entirely. A thin, flexible tube called a catheter is passed through the vagina and cervix, and sperm are injected directly into the uterus. This puts them much closer to the fallopian tubes, where fertilization happens.
Before the sperm go anywhere near the uterus, they go through a preparation process called sperm washing. The semen sample is mixed with a special fluid and spun in a centrifuge, which separates healthy, actively moving sperm from the rest of the ejaculate, including dead sperm, fluid, and other cellular debris. The result is a small, concentrated sample of the best-quality sperm available. The specific washing technique depends on the sample quality. When sperm counts and movement are normal, a simpler method works fine. When there are sperm quality issues, labs use density-based separation techniques that recover a greater number of healthy sperm.
What a Typical Cycle Looks Like
An IUI cycle revolves around one critical window: ovulation. Because sperm need a viable egg to fertilize, the insemination has to happen right around the time an egg is released from the ovary. Getting that timing right is the central challenge of the entire process.
There are two main approaches. In an unmedicated cycle, you track ovulation using at-home urine test kits that detect a surge in luteinizing hormone (LH), the signal your body sends to trigger egg release. In a medicated cycle, fertility drugs help stimulate the ovaries to produce one or more eggs, and your clinic monitors follicle development with ultrasounds. A hormone injection may be used to trigger ovulation at a precise time so the insemination can be scheduled accordingly.
The insemination itself is quick. Most people describe it as similar to a Pap smear. The catheter is inserted, the sperm sample is injected, and the whole thing takes just a few minutes. You can typically return to normal activities the same day. Some light spotting or cramping afterward is common and not a cause for concern.
Who IUI Is Best Suited For
IUI works best when sperm can reach the egg but something is making that journey harder than it should be. Common reasons people try IUI include mild male factor infertility (lower sperm count or reduced motility), cervical issues that create a hostile environment for sperm, unexplained infertility where no clear cause has been identified, or situations where donor sperm is being used. Single individuals and same-sex couples also use IUI with donor sperm as a first-line option.
IUI is generally not recommended when both fallopian tubes are blocked, when there is severe male factor infertility, or when other conditions make it unlikely that sperm and egg will successfully meet even with the shortened distance. In those cases, IVF is typically a better starting point.
Success Rates by Age
Per-cycle success rates for IUI are modest compared to IVF, but the lower cost and simpler process make it a reasonable first step for many people. Age is the single biggest factor in how well it works:
- Under 35: Around 15 to 20% per cycle
- Ages 35 to 37: Roughly 10 to 15% per cycle
- Ages 38 to 40: Approximately 5 to 10% per cycle
- Over 40: Typically 2 to 5% per cycle
These numbers mean most people don’t get pregnant on the first try. Cumulative odds improve over multiple cycles, which is why fertility specialists often recommend trying three to six rounds of IUI before considering other options. That said, for people over 38 or so, the relatively low per-cycle rates sometimes make it more practical to move to IVF sooner rather than spending months on repeated IUI attempts.
How IUI Compares to IVF
The biggest differences between IUI and IVF come down to complexity, cost, and effectiveness. IUI places sperm in the uterus and lets fertilization happen naturally inside the body. IVF removes eggs from the ovaries, fertilizes them in a lab, and transfers an embryo back into the uterus. IVF has significantly higher success rates per cycle, especially for older patients or those with more complex fertility issues.
Cost reflects that gap in complexity. An IUI cycle without medication can run upward of $1,000. Adding oral or injectable fertility drugs brings the total to roughly $1,100 to $3,000 per cycle. A single IVF cycle, by contrast, costs between $12,000 and $20,000 before medications, which add another $2,000 to $6,000. There was a time when most fertility specialists recommended trying several IUI cycles before moving to IVF, but that approach has shifted. For many patients, particularly those over 35, the higher per-cycle success of IVF can make it the more cost-effective choice from the start when you factor in multiple failed IUI attempts.
Risks and Side Effects
The insemination procedure itself carries very few risks. Mild cramping during or after the catheter insertion is the most common complaint, and it passes quickly. Infection is possible but rare.
Most of the risks associated with IUI actually come from the fertility medications used alongside it, not the procedure itself. One significant concern is multiple pregnancy. When fertility drugs stimulate the ovaries, they can cause more than one egg to be released. The rate of twins and higher-order multiples with ovarian stimulation has been reported at over 20 times and 100 times greater, respectively, than with natural conception. Multiple pregnancies carry higher risks for both the pregnant person and the babies, including premature birth and low birth weight.
A less common but more serious medication-related risk is ovarian hyperstimulation syndrome, or OHSS. This happens when the ovaries overreact to fertility drugs, particularly injectable ones. Mild cases cause bloating, nausea, and abdominal discomfort, and usually resolve within about a week. Severe OHSS is uncommon but can involve rapid weight gain (more than 2 pounds in 24 hours), difficulty breathing, decreased urination, and in rare cases, blood clots or kidney problems. Your clinic monitors follicle development during medicated cycles partly to reduce this risk. If too many eggs are developing, the cycle may be canceled to avoid complications.