A good candidate for IUI is typically someone with at least one open fallopian tube, a partner (or donor) with adequate sperm counts, and a fertility challenge that doesn’t require the more intensive process of IVF. IUI works by placing sperm directly into the uterus around the time of ovulation, bypassing several natural barriers. It’s a common first step in fertility treatment because it’s less invasive, less expensive, and effective for a specific set of diagnoses.
Conditions Where IUI Works Best
IUI is a strong option for several well-defined fertility diagnoses. The most common include:
- Unexplained infertility. When standard testing hasn’t revealed a clear cause, IUI paired with ovulation-stimulating medication is often the first treatment tried.
- Mild male factor infertility. If sperm count, motility, or shape are slightly below normal but not severely impaired, IUI concentrates the healthiest sperm and delivers them closer to the egg.
- Cervical factor infertility. Thick cervical mucus, scarring, or other cervical issues can block sperm from reaching the uterus. IUI bypasses the cervix entirely.
- Ovulatory disorders. Conditions like PCOS, where ovulation is irregular or absent, respond well to IUI when combined with medication to stimulate egg development.
- Mild to moderate endometriosis. IUI is typically recommended for earlier-stage endometriosis (stages I and II), especially after surgical treatment.
- Donor sperm. For single individuals or couples using donor sperm, IUI is the most common method of achieving pregnancy.
The Fallopian Tube Requirement
At least one fallopian tube needs to be open and functional for IUI to work. The egg and sperm still meet in the fallopian tube during IUI, so a complete blockage on both sides rules out the procedure. Before starting treatment, most doctors order a hysterosalpingogram (HSG), an imaging test that checks whether the tubes are open.
If you have one blocked tube and one open tube, you can still be a candidate. If an HSG suggests both tubes are blocked, doctors often recommend a follow-up test before jumping to IVF, since false-positive readings for blockage occur in up to 15% of cases. Temporary spasm or mucus plugging during the test can make an open tube look closed.
Sperm Count Thresholds
Before IUI, the sperm sample is washed and concentrated to isolate the most motile sperm. The total number of progressively moving sperm after this process, called the post-wash total motile sperm count, is one of the strongest predictors of success. A count of 10 million or higher after washing is generally considered the threshold for a reasonable chance of pregnancy. When the post-wash count drops below 1 million, pregnancy rates fall to roughly 2% per cycle, making IVF a better option at that point.
If your partner’s semen analysis shows borderline numbers, the post-wash results will determine whether IUI is worth pursuing. Some men with lower raw counts still produce an adequate sample after processing.
How Age Affects Your Candidacy
Age is one of the biggest factors in whether IUI makes sense. Per-cycle pregnancy rates in a large analysis of over 4,200 IUI cycles break down roughly like this:
- Ages 25 to 29: about 13% per cycle
- Ages 30 to 34: about 11% per cycle
- Ages 35 to 39: about 9% per cycle
- Ages 40 to 41: about 9% per cycle
- Ages 42 to 43: about 6% per cycle
- Over 43: about 3.5% per cycle
Success rates stay relatively stable up to age 40, even over multiple cycles. After 43, the per-cycle odds drop sharply enough that many reproductive endocrinologists recommend moving to IVF sooner rather than spending months on IUI. For people under 35, IUI is a reasonable first-line approach. For those over 40, it can still work, but the window for trying is shorter, and fewer cycles are typically recommended before escalating treatment.
IUI for PCOS
PCOS is one of the most common causes of ovulatory infertility, and IUI paired with ovulation-stimulating medication tends to perform well for this group. In a study of over 1,000 IUI cycles in women with PCOS, the clinical pregnancy rate was about 22% per cycle, which is notably higher than the general IUI average. The cumulative live birth rate after up to four cycles reached approximately 31% per patient.
About 98% of pregnancies in PCOS patients occurred within the first three IUI cycles. If you have PCOS and don’t conceive in three rounds, success in subsequent rounds drops considerably, and it may be time to discuss alternatives.
IUI for Endometriosis
Endometriosis is staged from I (minimal) to IV (severe), and your stage matters for IUI candidacy. In patients with stage I or II endometriosis who underwent IUI with ovarian stimulation after surgery, the cumulative pregnancy rate was about 65%, with a live birth rate around 57%. For stages III and IV, those numbers dropped to roughly 46% and 41% respectively.
Milder endometriosis responds meaningfully better to IUI. If you have stage III or IV disease, IUI can still work, but the success gap is large enough that your doctor may weigh IVF more seriously, especially if other factors like age are also working against you.
How Many Cycles Before Moving On
IUI is not a procedure most people try indefinitely. For women under 35, fertility specialists typically recommend three rounds of IUI before considering IVF, though in some cases that number extends to six. For women over 35, the recommendation is usually fewer cycles because the time spent on lower-probability attempts carries a real cost as egg quality continues to decline.
The data consistently shows that most IUI pregnancies happen in the first three cycles. If three well-timed rounds with medication haven’t worked, the odds of the fourth or fifth cycle succeeding are substantially lower. At that point, the conversation usually shifts to IVF, which has higher per-cycle success rates but is more physically and financially demanding.
Timing and What to Expect
Precise timing is critical to IUI success. The procedure should happen within 24 to 36 hours after either a natural LH surge (detected by an ovulation kit) or a trigger shot that induces ovulation. In natural cycles, ovulation occurs roughly 25 to 56 hours after the LH surge begins. With a trigger shot, the window narrows to 36 to 48 hours. Studies show that insemination one day after the LH rise produces significantly higher pregnancy rates than waiting two days.
During the cycle, you’ll have monitoring appointments with ultrasound to track follicle development. If you’re taking ovulation medication, these visits help your care team decide when to trigger ovulation or tell you to use an ovulation predictor kit. The insemination itself takes only a few minutes and feels similar to a Pap smear. Most people return to normal activities the same day.
Who Is Not a Good Candidate
IUI is unlikely to be the right choice if both fallopian tubes are blocked, if the post-wash sperm count falls below 1 million, or if you’re over 43 and want to maximize your chances per cycle. Severe male factor infertility, where sperm counts or motility are very low, typically requires IVF with a technique that injects a single sperm directly into the egg. Similarly, conditions that significantly distort the uterine cavity, like large fibroids, may need to be addressed before IUI can be effective.
People who have already completed three to six unsuccessful IUI cycles are also generally no longer good candidates for continuing the same approach. At that point, the underlying issue likely requires a more targeted intervention than IUI can provide.