IUI Success Rates: The Honest Numbers by Age and Diagnosis

Your reproductive endocrinologist has just suggested intrauterine insemination, or your first cycle came back negative and you are looking up what was supposed to happen. The numbers you are about to find online are wildly inconsistent. The version of the conversation I want to have here is the one I have in clinic. That means the per-cycle ranges, the cumulative math, and the diagnoses laid out plainly rather than tucked under marketing language.

The short version sits in two sentences. The IUI success rate by age is real but modest, typically between 8 and 20 percent per cycle under 35 and falling steeply after 38. What actually matters for the decision you are making is your cumulative chance across three cycles, not the headline number from any single one. The rest of this post is the longer version of those two sentences, with the trial data, the diagnosis-specific numbers, and the decision frame attached.

Why a single "IUI success rate" number is misleading

When you search for what is IUI success rate, the figures you find range from 5 percent to 25 percent per cycle. That spread is not a sign that the data is unreliable. It is a sign that "success rate" is doing different jobs in different places.

A few things drive the variation. Age is the biggest variable, and most clinics quote their headline number for under-35s because that is where their best outcomes sit. Diagnosis is the second variable. A donor-sperm cycle in someone without female-factor infertility looks very different from a cycle in someone with mild male-factor infertility and an AMH of 1.2 ng/mL.

The third variable is what the clinic is counting. Clinical pregnancy on an ultrasound at six to seven weeks is a higher number than ongoing pregnancy at twelve weeks, and ongoing pregnancy is a higher number than live birth. The fourth is the denominator. Per cycle started is a smaller number than per cycle that reached insemination, which is itself smaller than per patient across multiple cycles.

A clinic quoting "20 percent" may be reporting clinical pregnancy in under-35s with unexplained infertility. If you are 38 with mild male factor, that is not your number. When a clinic shows you a stat sheet, your job, and I will come back to this, is to ask which definition and which population.

Per-cycle live birth by age: the honest ranges

I want to place the by-age ranges in their own block so you can find them quickly. These are pulled from large registry data (HFEA in the UK, SART in the US) and the FAST-T/AMIGOS trial of unexplained infertility treatments published in NEJM in 2015.¹^,⁶

Under 35: roughly 10 to 20 percent per cycle live birth in most published series, with letrozole-IUI and clomid-IUI sitting near the lower middle of that range and donor-sperm cycles in non-infertile recipients sitting near the top.

35 to 37: roughly 10 to 15 percent per cycle. The same protocols are doing slightly less work because oocyte quality has begun to drift.

38 to 40: roughly 5 to 10 percent per cycle. This is the band where the FORT-T trial (Goldman 2014) showed that an accelerated path to IVF reduced time-to-live-birth compared with the standard IUI-first ladder.³

41 to 42: roughly 2 to 5 percent per cycle. The slope is now steep enough that most US REs will counsel toward IVF or a donor-egg conversation rather than a third IUI.

Over 42: generally under 2 percent per cycle. IUI is rarely the right tool here. The math, the time, and the cost all point elsewhere.

Those are per-cycle live birth ranges, not clinical pregnancy. If your clinic's number is higher than the upper end of the band for your age, the chances are they are quoting clinical pregnancy or under-35-only data. Ask which.

Cumulative success across three to four cycles

Per-cycle numbers are not what you should be planning around. Cumulative numbers are.

The cycles are roughly independent through the first three to four attempts, which means probabilities multiply rather than add. If your per-cycle live birth is 12 percent, your cumulative live birth across three cycles is roughly 32 percent (1 minus 0.88 cubed), not 36 percent. Across four cycles it is roughly 40 percent. The curve flattens after that, which is why most guidelines, including NICE NG156 in the UK and the ASRM committee opinion on IUI in the US, recommend reassessment after three to six cycles.⁷

This is the math behind the IUI success rate calculator pages you may have already found. The shape is more important than any single number. Most of the pregnancies that will happen with IUI happen in the first three cycles. The fourth cycle still adds odds. The fifth and sixth add less, and at some point the cost-time math switches over to favouring IVF.

I cover the stopping rule in more depth at how-many-iuis-before-moving-on.

Diagnosis-specific numbers

Age is the largest variable, but diagnosis is the second largest. Here is how the published numbers map by indication.

Unexplained infertility: the FAST-T/AMIGOS trial randomised 900 couples with unexplained infertility to letrozole-IUI, clomid-IUI, or gonadotropin-IUI for up to four cycles. Per-cycle conception rates were 8.6 percent for letrozole, 9.0 percent for clomid, and 17.5 percent for gonadotropin.¹ The gonadotropin arm achieved the highest pregnancy rate but with a 32 percent multiple-pregnancy rate, which is the reason most US clinics have moved away from gonadotropin-IUI entirely. Letrozole and clomid are roughly equivalent here and either is a reasonable starting protocol.

PCOS: when ovulation is achieved with letrozole, IUI outcomes in PCOS are broadly comparable to unexplained infertility cohorts. The PALM/PPCOS-II trial (Legro 2014, NEJM) showed letrozole outperforming clomid for live birth in PCOS specifically.² Deeper PCOS-specific data lives in iui-with-pcos-data.

Mild male factor: per-cycle live birth tracks the post-wash total motile count. Above 10 million it looks like an unexplained-infertility curve. Between 5 and 10 million it drops modestly. Below 5 million it drops sharply, and most clinics will pivot the conversation toward IVF with ICSI. I cover the thresholds in detail in iui-sperm-count-requirements.

Endometriosis stage I or II: roughly comparable to unexplained infertility cohorts. Stage III or IV with anatomical distortion is a different conversation; IVF typically outperforms IUI there.

Donor sperm with no female-factor infertility: these are the highest IUI numbers in the literature, often 15 to 20 percent per cycle in under-35s. This is the cohort that drives the upper end of clinic marketing numbers and is rarely your cohort if you are reading this after a workup that found something.

Cervical factor or sexual dysfunction preventing conception: a strong IUI indication; the procedure bypasses the barrier directly.

What changes the numbers within your age band

Once your age and diagnosis are set, several variables move the per-cycle number within your band. These are the levers your RE is adjusting between cycles, and you are entitled to ask which ones are being adjusted and why.

The first lever is the number of mature follicles at the time of trigger. One follicle is the baseline. Two follicles modestly improves per-cycle pregnancy with a meaningfully higher twin risk; this is the data behind the 2 follicles IUI success rate searches. Three or more follicles bumps the per-cycle pregnancy a little further but pushes multiple-pregnancy risk into territory that most modern clinics will not accept. Some clinics cancel the cycle and convert to abstinence at three or more mature follicles, particularly in PCOS. Merviel and colleagues' analysis of more than a thousand IUI cycles is one of the better breakdowns of how follicle count and other predictors translate to per-cycle outcomes.⁴

The second is the post-wash total motile sperm count on the day of insemination, which I discussed above.

The third is endometrial thickness at trigger. Most clinics want over 7 mm. Thinner linings are associated with lower per-cycle pregnancy in observational series, and clomid in particular can thin the endometrium in some people, which is one reason letrozole has become the more common oral agent.

The fourth is timing. The literature supports a single insemination 24 to 36 hours after the hCG trigger. Double insemination (two procedures in the same cycle) shows minimal additive benefit in most meta-analyses and roughly doubles the cost. Most clinics no longer offer it as standard.

The fifth is medication choice. Letrozole versus clomid is roughly a wash for IUI in unexplained infertility. In PCOS specifically, letrozole outperforms clomid on live birth (PALM, Legro 2014).² The clomid and IUI success rate question is well-studied. The honest answer is that for most diagnoses the two are interchangeable, with letrozole preferred for PCOS and clomid still used at clinics where letrozole is harder to obtain.

What does not meaningfully change the numbers

The internet is full of things people do after IUI that are not on this list. None of these have a meaningful effect on per-cycle live birth, despite how much air time they get.

• Bed rest after IUI beyond about ten minutes
• Sex after IUI (it does not hurt, but does not clearly help)
• Specific dietary changes in the two weeks after the procedure
• Most over-the-counter supplements taken specifically post-IUI
• Acupuncture for IUI specifically (the data is mixed; the better evidence is for IVF transfer)

I name these because the loneliness of the two-week wait pushes a lot of readers toward rituals. Rituals can help your psychology and the data on that is real, but they do not change the underlying probability of the cycle. Knowing this is, in my clinical experience, more useful than not knowing it.

How to read your clinic's stat sheet honestly

Most clinics publish success rates. The headline number is rarely your number, and the questions you can ask before signing a treatment plan are simple.

1. Are you reporting clinical pregnancy or live birth?
2. What is the denominator: per cycle initiated, per cycle to insemination, or per patient?
3. What age band does this number represent?
4. What is the diagnosis mix in that age band? A clinic doing mostly donor-sperm IUIs will look better than one doing complex cases.
5. How many cycles per patient does the dataset cover, and what is the cumulative live birth across those cycles?

A clinic that answers these clearly is being honest with you. A clinic that deflects or uses qualifiers like "best-in-class" without numbers is not.

Common worries: what is normal, what is a red flag

I see the same handful of questions land in the first or second cycle, and they deserve direct answers.

"My number is lower than what the internet promised." Most internet numbers are clinical pregnancy under 35. Live birth is typically 10 to 20 percent lower than clinical pregnancy because of early loss, biochemical pregnancy, and the gap between an ultrasound at six weeks and a baby at term. If your number is in the live-birth band I listed for your age, your number is normal.

"My first IUI was negative, what does the second IUI success rate look like?" Independence is the right framing. The cycles are roughly independent through three to four attempts; your per-cycle probability does not fall after cycle one. Some readers find this reassuring (cycle two is just as good as cycle one) and others find it frustrating (cycle one was not predictive). Both reactions are normal. The first time IUI success rate searches and second IUI success rate searches are looking for the same thing. The honest answer is that the per-cycle probability is similar across the first three attempts.

"How early can I test, and does the trigger shot confuse it?" The trigger shot contains hCG, which can produce a false-positive home pregnancy test for up to 10 to 14 days. Most clinics do a beta-hCG blood draw 14 days after IUI. Earlier home tests can read positive from residual trigger and break your heart twice when the beta comes back negative. The cleanest version of the two-week wait is to wait.

"Three IUIs have failed; is something wrong with me?" A run of three independent failures is statistically meaningful enough to be the conversation, not the catastrophe. It is the moment to revisit the diagnosis, the protocol, and whether IVF is the next rational step. I cover this in third-iui-failed-what-now and when-to-skip-iui-go-ivf.

A simple decision frame

Once you have your age band, your diagnosis, and the per-cycle and cumulative numbers, the IUI question collapses to a small decision tree. This is roughly how I walk patients through it.

Under 35, no severe factor: three to four IUI cycles is the standard ladder before considering IVF. Cumulative live birth across that ladder is in the 30 to 40 percent range for most diagnoses. There is no rush; the math is on your side.

Age 35 to 37: two to three cycles is the more common ceiling. Each cycle still has reasonable odds, but reassessment after three failed cycles is the standard.

Age 38 to 40: one to two IUI cycles before IVF is now the more common pattern, supported by FORT-T data on faster-to-IVF in this age band.³ The cost is real and the per-cycle odds are still meaningful, but the time pressure is also real.

Age 41 and over: most REs go directly to IVF or to the donor-egg conversation. IUI is rarely the right tool here.

The full decision frame across natural, IUI, and IVF lives in natural-vs-iui-vs-ivf-decision.

What you can do this cycle

Two practical pieces.

The first is to ask your RE for your specific per-cycle live-birth estimate and your projected cumulative live birth across the recommended cycle count. They have your AMH, your antral follicle count, your partner's semen analysis, and your age. The estimate they give you is more useful than any online calculator.

The second is to track this cycle in a way that lets you compare cycle 1 to cycle 2 without trusting memory. Trigger date, follicle count at trigger, endometrial thickness, post-wash total motile count, and the date of insemination are the variables that matter. If cycle 1 was negative, those data points are the conversation with your RE before cycle 2. The IUI success rate by age you see on a brochure is a population number; the one your tracking produces is yours.

What's next

• If you are in cycle 1 and waiting on the beta: the two-week wait, luteal phase explained
• If you have PCOS and want the diagnosis-specific data: iui-with-pcos-data
• If your partner's semen analysis is the variable in question: iui-sperm-count-requirements
• If cycle 1 was negative and you are looking at cycle 2: second-iui-what-changes
• If three cycles have failed: third-iui-failed-what-now and when-to-skip-iui-go-ivf
• If you are evaluating the whole ladder: natural-vs-iui-vs-ivf-decision

Related in this cluster

• Medicated vs Unmedicated IUI: Which One You're Doing and Why

Sources

1. Diamond MP, Legro RS, Coutifaris C, et al. Letrozole, gonadotropin, or clomiphene for unexplained infertility. New England Journal of Medicine 2015;373(13):1230-1240. Link
2. Reindollar RH, Regan MM, Neumann PJ, et al. A randomized clinical trial to evaluate optimal treatment for unexplained infertility: the Fast Track and Standard Treatment (FASTT) trial. Fertility and Sterility 2010;94(3):888-899. Link
3. Goldman MB, Thornton KL, Ryley D, et al. A randomized clinical trial to determine optimal infertility treatment in older couples: the Forty and Over Treatment Trial (FORT-T). Fertility and Sterility 2014;101(6):1574-1581.e2. Link
4. Merviel P, Heraud MH, Grenier N, et al. Predictive factors for pregnancy after intrauterine insemination (IUI). Fertility and Sterility 2010;93(1):79-88. Link
5. ESHRE Guideline Group on Unexplained Infertility. ESHRE guideline: unexplained infertility. Human Reproduction Open 2023;2023(1):hoad007. Link
6. Human Fertilisation and Embryology Authority (HFEA). Fertility treatment 2021: preliminary trends and figures. Link
7. National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. NICE guideline NG156. 2013, updated 2017. Link