Intrauterine Insemination or IUI: What It Actually Is

You have either just been told that intrauterine insemination or IUI is your next step, or you are reading ahead of a consult. Either way, you want the whole picture before you sit across from a reproductive endocrinologist. Most people I see in clinic arrive imagining something much more invasive than the procedure actually is, and leave surprised it was over before they fully settled into the chair.

This is the pillar piece for the IUI section of the library. It covers what the procedure is, who it helps and who it does not, the honest per-cycle numbers, how it differs from IVF, and where it sits on the broader treatment ladder. The day-of walkthrough, the pain question, the cost breakdown, and the post-procedure window each have their own dedicated post linked at the bottom.

What intrauterine insemination or IUI actually is

Intrauterine insemination is a small office procedure that places a washed, concentrated sperm sample directly into the uterus through a thin catheter on the day you ovulate. The goal is to shorten the trip motile sperm have to make and increase the number that reach the fallopian tubes, where fertilisation would naturally happen. It is sometimes called artificial insemination. That older term also covers cervical and vaginal approaches that modern fertility clinics rarely use; almost every clinic today does the intrauterine version because it produces better pregnancy rates.

IUI is not IVF. No egg is retrieved, no fertilisation happens outside the body, and no embryo is transferred. You ovulate, the sperm is delivered closer to the egg, and the rest of the process happens the way it would in any other cycle.

The procedure itself takes about five minutes. Most of your appointment is paperwork, undressing, and the post-procedure rest period. The lab work that prepares the sample takes longer than the insemination.

Who IUI is for

The National Institute for Health and Care Excellence (NICE) guideline NG156 is the main UK reference for fertility treatment. The American Society for Reproductive Medicine (ASRM) committee opinions converge on a similar list of indications.¹,⁵ IUI is typically offered when at least one of the following is true.

• Mild male-factor infertility, defined by a post-wash total motile sperm count above roughly 5 to 10 million. Different clinics use slightly different thresholds. Below that range, most reproductive endocrinologists recommend skipping straight to IVF with ICSI.
• Unexplained infertility after a full workup and a year of trying, or six months if the female partner is 35 or older.
• Cervical-factor infertility, where the cervical mucus is hostile to sperm or the cervix is scarred from a previous procedure.
• Same-sex female couples or single people using donor sperm: This is by far the largest growth area for IUI in many clinics.
• Ovulatory disorders, including polycystic ovary syndrome (PCOS), almost always paired with letrozole or clomiphene to produce a more predictable, single-dominant follicle.
• Mild endometriosis, stage I or II, where the anatomy is preserved but the pelvic environment is suboptimal.
• Sexual dysfunction or anatomical issues that prevent vaginal intercourse on the right days of the cycle.

When I am explaining IUI in clinic, I usually frame it as a small mechanical assist. It helps the sperm find the egg. It does not do anything for egg quality, tubal function, the embryo itself, or implantation.

Who IUI is not for

There are clear situations where IUI is not the right next step, and pretending otherwise burns time and money you may not have.

• Bilateral tubal blockage: If neither fallopian tube is open, the sperm and egg have nowhere to meet. IVF, which bypasses the tubes entirely, is the answer.
• Severe male-factor infertility: With a post-wash total motile count under about 5 million, IUI success rates fall sharply, and most clinics recommend IVF with intracytoplasmic sperm injection (ICSI) instead.
• Moderate to severe endometriosis with anatomical distortion.
• Diminished ovarian reserve in someone over 38 or 40, where the math on burning two or three cycles on IUI before reaching IVF rarely works out, as the FORT-T (Forty and Over Treatment Trial) data made clear.⁴

Part of the consultation I have with new IUI patients is the honest version of this list. If you are sitting in the second group, it is better to know now than to find out after cycle three.

What the procedure day looks like, briefly

I cover the full minute-by-minute in a separate post, but here is the shape of the day in sixty seconds.

The night before, you take a trigger shot, usually Ovidrel (recombinant human chorionic gonadotropin, hCG) at 250 micrograms subcutaneously. In an unmedicated cycle, you instead detect your luteinising hormone (LH) surge on an ovulation predictor kit (OPK) and schedule the IUI for the next morning. Your partner produces a sample at home or in the clinic about one to two hours before the procedure, or a thawed donor sample is prepared. The lab "washes" the sample, which means separating motile sperm from seminal fluid, dead sperm, and debris using a density gradient or swim-up technique.

You arrive, change into a gown waist-down, and lie on the exam table the way you would for a Pap smear. A speculum goes in, a thin flexible catheter is threaded through the cervix into the uterine cavity, and the washed sample is slowly injected. The catheter and speculum come out. You lie flat for five to fifteen minutes depending on the clinic's protocol, then get dressed and go home.

For the longer walkthrough, see Your First IUI: What the Day Actually Looks Like. For the pain question specifically, see Does IUI Hurt.

Natural cycle versus medicated cycle IUI

There are three broad ways to run an IUI cycle, and which one your clinic chooses is one of the most important conversations you can have before you start.

Unmedicated, or natural cycle IUI relies on your own LH surge to trigger ovulation. You usually grow one egg. This works for younger people with regular ovulation, particularly same-sex couples and single people using donor sperm where the male side is not the issue. The cycle is cheaper, simpler, and gentler on the body, but it depends on a reliable surge.

Medicated IUI with oral agents uses letrozole or clomiphene from cycle days three to seven, with one or more monitoring scans and usually a trigger shot when a lead follicle reaches roughly 18 to 22 millimetres. This is the protocol most US clinics use for unexplained infertility and PCOS. Targets are typically one to three mature follicles. Letrozole has gradually become first-line for ovulation induction in PCOS based on the PCOS PPCOS-II trial and is supported in current ASRM and NICE recommendations.¹,⁵

Medicated IUI with injectable gonadotropins uses follicle-stimulating hormone preparations like Gonal-F, Follistim, or Menopur to drive multiple follicles. Per-cycle pregnancy rates are higher. But the FAST-T (Assessment of Multiple Intrauterine Gestations from Ovarian Stimulation, also called AMIGOS) trial, published in the New England Journal of Medicine in 2015, showed an unacceptable triplet rate compared with letrozole or clomiphene.² Most US clinics have moved away from gonadotropin-IUI for that reason, except in carefully selected cases.

A full comparison lives in the dedicated medicated versus unmedicated IUI post.

The honest numbers

This is where most online sources oversell. I want to give you the figures I actually quote in clinic.

Per-cycle live birth from IUI runs roughly 5 to 20 percent, with the range collapsing toward the lower end as age rises and the diagnosis becomes more complex. The FAST-T trial in unexplained infertility found clomiphene-IUI producing about 9.0 percent per-cycle pregnancy, letrozole-IUI about 8.6 percent, and gonadotropin-IUI higher but with the multiples problem already mentioned.² The Goldman 2014 per-cycle pregnancy data and the broader analysis published the same year in Fertility and Sterility put live birth on IUI in the same band.³

What matters more than any one cycle is the cumulative figure across three to four cycles, which is roughly two to three times the per-cycle number. This is why IUI is designed as a loop. The Cochrane review on IUI for unexplained subfertility by Veltman-Verhulst and Hughes, the most recent comprehensive synthesis, supports this cumulative framing.⁶

The chances of success with IUI break down further by age and diagnosis in IUI Success Rates by Age and IUI With PCOS: What the Data Says. The IUI percentage of success quoted in clinic brochures often blends age groups in ways that flatter the average. The post on age-stratified numbers is where I would point you for the version you can actually use.

What IUI does and does not fix

The clearest way to think about IUI is in terms of what it changes mechanically. It changes the trip the sperm has to make. It increases the concentration of motile sperm at the right anatomical site. It allows the timing of insemination to be locked to the hour rather than guessed from an OPK.

It does not improve egg quality. It does not open blocked tubes. It does not help an embryo implant. It does not change embryo genetics. This is why IUI success rates plateau around cycle three or four. If the limiting factor was the trip past the cervix, IUI usually solves it in the first two or three cycles. If it has not worked by cycle four, the limiting factor is almost always somewhere IUI cannot reach, and the conversation shifts toward IVF.

Cost orientation

The US per-cycle cost typically runs $500 to $4,000, with most clinics clustering at $1,500 to $3,000 for a medicated IUI. Unmedicated cycles at low-cost clinics with minimal monitoring can sit below $500. Gonadotropin-IUI commonly runs $3,000 to $5,000 because the medications alone are expensive. Insurance coverage in the US is highly variable. Some states have fertility mandates that include IUI; many do not. In the UK, NHS commissioning of IUI through Integrated Care Boards varies widely.

The full breakdown lives in IUI Cost: Per Cycle, With and Without Insurance, including line items and what to ask the billing office before cycle one.

How IUI fits on the treatment ladder

The traditional ladder runs timed intercourse, then medicated timed intercourse, then IUI, then IVF. Each step adds intervention, cost, and per-cycle odds. Skipping rungs is sometimes the right call.

The FORT-T (Forty and Over Treatment Trial) by Goldman and colleagues was published in Fertility and Sterility in 2014. It randomised couples where the female partner was 38 to 42 to one of three strategies: clomiphene-IUI then IVF, gonadotropin-IUI then IVF, or immediate IVF.⁴ The immediate-IVF arm produced live births faster than either IUI-first arm. The FAST-T trial in unexplained infertility came to a related conclusion in a younger group, with letrozole-IUI and clomiphene-IUI performing similarly and gonadotropin-IUI not justifying its multiples risk.²

In clinic, the practical translation runs like this. Under 35 with no severe factor, three to four IUI cycles is a reasonable plan. From 35 to 37, two to three. From 38 onward, the math often favours going to IVF sooner, and for someone over 40 I usually have a direct conversation about skipping IUI entirely. None of this is a moral verdict on choosing one path over another, but the data is fairly clear about which paths get more people to a live birth in less time.

The decision frame lives in Natural Versus IUI Versus IVF: How to Decide.

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

A few questions come up in almost every post-IUI follow-up.

Mild cramping, light spotting, slight discharge in the hours after IUI: Normal. The catheter brushed the cervix on the way through and the uterus is responding to a small volume of fluid being injected. It does not mean the procedure failed.

Heavy bleeding, a fever over 100.4 degrees Fahrenheit (38 Celsius), severe one-sided pelvic pain: Call the clinic. These are uncommon, but they are how pelvic infection and ovarian hyperstimulation syndrome (OHSS) can present, and they need to be ruled out promptly.

"Did the sperm fall out when I stood up?" No. The sample is placed past the cervix, into the uterine cavity. Gravity is not the enemy here. You can walk, drive, go back to work.

"Should I lie down for ten minutes after?" Clinic policy varies, and the evidence is weak. The randomised trial by Custers and colleagues in BMJ found no benefit to immobilisation over immediate mobilisation. If the clinic asks, do it. If it does not, it is not going to change your odds.

What to ask before your first IUI

Five questions cover most of what you need to know going into cycle one.

1. What protocol are we using (natural cycle, letrozole, clomiphene, or injectables), and why is that the choice for me?
2. How many follicles are we targeting at trigger, and what is the cancellation threshold if we get too many?
3. What is my partner's post-wash total motile count, and is it in the range your clinic considers worthwhile for IUI?
4. How many IUI cycles are we planning before we reassess and consider moving to IVF?
5. What does the cycle cost out of pocket, what does insurance cover, and what gets refunded if the cycle is cancelled?

Write the answers down. Cycle one is when most patients are absorbing too much at once to remember the specifics, and the answers matter for the cycle two and three conversations. Intrauterine insemination or IUI is a mechanical assist, not a magic bullet; the cycle plan you build from these answers is what determines whether the assist gets used well.

What's next

• If you are heading into your first IUI cycle now → Your First IUI: What the Day Actually Looks Like
• If pain is your main worry → Does IUI Hurt: What to Expect Physically
• If you are past the procedure and managing the wait → After Your IUI: What to Do and What to Avoid
• If cost is the deciding factor → IUI Cost: Per Cycle, With and Without Insurance
• If this cycle did not work and you are deciding what comes next → Failed IUI: What to Do Next
• If you are deciding whether to skip IUI and go to IVF → Natural Versus IUI Versus IVF: How to Decide

Sources

1. National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. NICE guideline NG156. Originally CG156, 2013; last updated 2017. https://www.nice.org.uk/guidance/ng156
2. Diamond MP, Legro RS, Coutifaris C, et al. Letrozole, gonadotropin, or clomiphene for unexplained infertility (AMIGOS/FAST-T). New England Journal of Medicine 2015;373(13):1230-1240. doi:10.1056/NEJMoa1414827. https://www.nejm.org/doi/full/10.1056/NEJMoa1414827
3. 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. doi:10.1016/j.fertnstert.2009.04.022. https://www.fertstert.org/article/S0015-0282(09)00731-1/fulltext
4. 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. doi:10.1016/j.fertnstert.2014.03.012. https://www.fertstert.org/article/S0015-0282(14)00254-0/fulltext
5. Practice Committee of the American Society for Reproductive Medicine. Use of exogenous gonadotropins for ovulation induction in anovulatory women: a committee opinion. Fertility and Sterility 2020;113(1):66-70. doi:10.1016/j.fertnstert.2019.09.020. https://www.asrm.org/practice-guidance/practice-committee-documents/
6. Veltman-Verhulst SM, Hughes E, Ayeleke RO, Cohlen BJ. Intra-uterine insemination for unexplained subfertility. Cochrane Database of Systematic Reviews 2016;(2):CD001838. doi:10.1002/14651858.CD001838.pub5. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001838.pub5/full