IUI

How intrauterine insemination works

IUI follows a consistent sequence whether the cycle is natural or stimulated:

1. Monitoring: transvaginal ultrasounds from cycle day 2 to 3, repeated every 2 to 3 days until follicles reach 17 to 20 mm.
2. Trigger: an hCG or GnRH agonist injection times final egg maturation. Insemination is scheduled 36 to 40 hours later.
3. Sperm preparation: density gradient centrifugation or swim-up technique separates motile sperm from seminal plasma and debris, producing 0.3 to 0.5 mL of concentrated sperm in culture medium.
4. Post-wash TMSC: the total motile sperm count after washing is calculated at this stage. This figure, not the raw semen analysis, determines whether the cycle proceeds.
5. Insemination: a thin catheter passes through the cervix into the uterine cavity and the sperm suspension is deposited directly. The procedure takes 5 to 10 minutes.
6. Luteal support: progesterone supplementation is typically prescribed. A serum hCG pregnancy test is performed 14 days after insemination.

Stimulated versus natural cycle IUI

Stimulated IUI uses letrozole, clomiphene, or low-dose FSH to develop one to two dominant follicles. Natural cycle IUI tracks spontaneous ovulation without medication.

Cycles are cancelled when three or more follicles of 14 mm or larger develop before the trigger. The risk of higher-order multiple pregnancy is too high to proceed.

A Cochrane review (Verhulst et al.) found mild stimulation modestly increased per-cycle rates versus natural cycle IUI, but not consistently enough to recommend stimulation universally.

Key differences:

1. Monitoring visits: 3 to 4 (natural) vs 4 to 6 (stimulated)
2. Medication: none (natural) vs letrozole, clomiphene, or low-dose FSH (stimulated)
3. Multiple pregnancy risk: equal to natural conception (natural) vs 15 to 25% twinning rate with FSH, lower with letrozole (stimulated)
4. Cycle cancellation risk: low (natural) vs 10 to 20% from over-response (stimulated)
5. Per-cycle success: 3 to 5 percentage points lower (natural) vs reference standard (stimulated)

Intrauterine insemination success rates: what the data shows

Per-cycle pregnancy rates vary by age, diagnosis, sperm quality, and stimulation protocol. These figures reflect published outcomes at established fertility centers:

1. Under 35: 15 to 22% stimulated / 11 to 18% natural cycle
2. 35 to 37: 12 to 17% stimulated / 8 to 14% natural cycle
3. 38 to 40: 8 to 14% stimulated / 5 to 10% natural cycle
4. 41 to 42: 5 to 10% stimulated / 3 to 7% natural cycle
5. Over 42: below 5% stimulated / below 3% natural cycle, with own eggs

Cumulative rates across multiple cycles are substantially higher. Published data show 40 to 50% of suitable candidates conceive within six stimulated IUI cycles.

Approximately 70 to 80% of all IUI pregnancies occur within the first three to four cycles. The incremental benefit of each additional cycle beyond four decreases progressively.

A widely cited randomized trial (Bhattacharya et al., 2008, The BMJ) found stimulated IUI produced pregnancy rates comparable to expectant management over six months in mild unexplained subfertility. Subsequent Cochrane analyses concluded IUI does outperform expectant management when evaluated over a full treatment course.

How sperm quality affects IUI outcomes

The post-wash total motile sperm count (TMSC) is the most clinically relevant metric. The pre-wash semen analysis alone does not determine suitability:

1. Above 10 million: per-cycle rates align with age-appropriate averages
2. 5 to 10 million: modestly reduced; IUI remains a reasonable first option
3. 2 to 5 million: significantly reduced; proceed with realistic expectations
4. Below 1 to 2 million: IUI is unlikely to succeed; IVF with ICSI is recommended

IUI with donor sperm consistently outperforms partner sperm IUI. In women under 35 using quality-screened donor samples, per-cycle clinical pregnancy rates of 18 to 25% are reported at established fertility centers.

Who is a good candidate for intrauterine insemination

1. Mild to moderate male factor: post-wash TMSC of 5 to 20 million. The post-wash count, not the pre-wash analysis, determines suitability.
2. Unexplained infertility: 12 months of trying without a cause (6 months if the female partner is 35 or older). IUI is typically offered for 3 to 6 cycles before IVF.
3. Single women and same-sex female couples using donor sperm: standard first-line treatment. Per-cycle success rates in women under 35 are among the highest for any IUI indication.
4. Cervical factor: hostile mucus, prior cervical surgery (LEEP, cone biopsy), or stenosis. IUI bypasses the cervix entirely.
5. Ovulatory dysfunction: PCOS or other anovulatory conditions where the patient responds to ovulation induction. IUI is combined with stimulation in this group.
6. Mild endometriosis (Stage I or II): evidence is mixed, but IUI with controlled ovarian stimulation is offered to younger women with minimal disease before escalating to IVF.
7. Sexual dysfunction: vaginismus, ejaculatory dysfunction, or any condition preventing consistent in vivo sperm deposition.
8. Any patient using donor sperm: placing sperm directly into the uterus maximizes the effective use of each donor sample, regardless of the underlying diagnosis.

Absolute contraindications to IUI

These conditions mean IUI cannot produce the intended outcome. Proceeding delays appropriate treatment without a realistic chance of success:

1. Bilateral tubal occlusion (confirmed on HSG or laparoscopy): at least one open, functional tube is required. Bilateral blockage is an absolute contraindication. IVF is indicated.
2. Post-wash TMSC below 1 million: the probability of IUI success approaches zero. IVF with ICSI is the correct treatment.
3. Premature ovarian insufficiency (POI): FSH persistently above 40 IU/L with absent or very irregular cycles. IUI with own eggs is not clinically appropriate. Donor egg IVF is the treatment of choice.
4. Active pelvic infection or untreated STI: proceeding risks ascending infection, endometritis, and pelvic inflammatory disease.
5. Significant uterine cavity distortion: submucosal fibroids (Type 0, 1, or 2) or endometrial polyps occupying the cavity should be treated hysteroscopically before any assisted reproduction.

When IVF is the more appropriate option

These situations do not make IUI physically impossible, but IVF produces substantially better outcomes:

1. Stage III or IV endometriosis: advanced disease impairs tubal function and the pelvic environment in ways IUI cannot address. IVF bypasses the peritoneal environment entirely.
2. Very low ovarian reserve (AMH below 0.5 ng/mL or AFC below 5): IUI does not improve the biological ceiling set by low reserve. IVF provides more diagnostic information and is typically more cost-effective per live birth.
3. Age over 42 with own eggs: per-cycle IUI success rates below 5% make the procedure a poor use of time. A frank discussion about realistic expectations, including donor eggs, is appropriate before committing to cycles.
4. Combined female and male factor: when both partners have contributing diagnoses, outcomes compound below what either factor would predict individually.
5. Repeated IUI failure (3 to 6 cycles): IVF is more cost-effective and produces significantly higher cumulative pregnancy rates. Continuing beyond this point rarely improves outcomes.

How many IUI cycles before moving to IVF

NICE and ESHRE recommend up to six stimulated IUI cycles before transitioning to IVF in eligible patients. This is based on cumulative data showing 40 to 50% of suitable candidates conceive within six cycles.

Earlier escalation is often clinically appropriate:

1. After 3 cycles if age is 38 or over: the cost-effectiveness balance shifts at this age, and delaying IVF has a measurable impact on live birth rates.
2. After 3 cycles if additional risk factors emerge: declining semen parameters, falling AMH, or newly identified pelvic pathology all justify earlier escalation.
3. At any point by patient choice: IUI is not a mandatory gateway to IVF. You are entitled to discuss escalation at any stage.

Each failed cycle should prompt a protocol review. Borderline post-wash counts, suboptimal stimulation dosing, or imprecise trigger timing are all adjustable before the next attempt.

Multiple pregnancy risk with stimulated IUI

Stimulated IUI carries a meaningful risk of twin or higher-order multiple pregnancy. Estimated twinning rates by protocol:

1. Natural cycle IUI: 2 to 3% (no added risk from stimulation)
2. Letrozole-stimulated: 8 to 12%
3. Clomiphene-stimulated: 10 to 15%
4. FSH-stimulated: 15 to 25%
5. General population (reference): 1 to 2%

Twin pregnancies carry significantly higher rates of preterm birth, low birth weight, gestational diabetes, preeclampsia, and cesarean delivery compared with singletons.

Cycles are cancelled when three or more follicles of 14 mm or larger are present at trigger assessment. This protocol reduces but does not eliminate multiple gestation risk.

Considering Intrauterine insemination abroad?

Patients pursue IUI outside their home country for three main reasons: legal eligibility not available at home, access to large regulated donor sperm pools with short wait times, and lower treatment costs.

Denmark is the primary destination for patients prioritizing donor sperm access. Its national sperm banks supply screened anonymous and identity-release donors internationally, with selection depth and genetic screening quality that few other countries match. Danish law has no eligibility restrictions based on marital status or sexual orientation. Most Danish clinics offer remote monitoring protocols, so patients travel only for the insemination itself, typically a one-to-two-day trip.

Cyprus is the most accessible European option for patients from the UK, Israel, the Middle East, and Eastern Europe who need legal eligibility not available at home. Regulated under the Bioethics Law 69(I)/2015, Cyprus permits IUI for single women and same-sex couples with no residency requirement. Direct flights connect to most EU, UK, and Gulf cities.

Mexico is cost-driven and practical for patients based in the US or Canada. Private fertility clinics in Mexico City, Guadalajara, and the Cancun-Riviera Maya corridor operate with no federal eligibility restrictions and English-speaking clinical teams experienced in treating international patients. Costs are substantially lower than comparable US treatment, and most American cities have direct short-haul flights.

Where cost, legal access, and donor availability are not factors, the decision narrows to the specific clinic's IUI outcomes data and the treating physician's experience with your diagnosis.

Frequently Asked Questions

Is IUI painful?

The procedure causes mild to moderate cramping, similar to menstrual discomfort, during catheter passage. Most patients describe the sensation as brief, with mild pelvic aching for a few hours afterward. No anesthesia is required, and most patients resume normal activity the same day.

What is the difference between IUI and IVF?

In IUI, washed sperm are placed into the uterus and fertilization occurs inside the body. In IVF, eggs are retrieved under sedation, fertilized in the laboratory, and embryos are transferred back. IUI is less invasive and less expensive but produces lower per-cycle success rates and requires open tubes and acceptable sperm parameters.

Can IUI be performed with frozen sperm?

Yes. Frozen partner or donor sperm is thawed, washed, and processed identically to a fresh sample. Post-thaw motility is typically lower than pre-freeze values, so your clinic will assess the post-wash TMSC after thawing before confirming the cycle proceeds.

How long does an IUI cycle take?

A stimulated cycle runs 12 to 16 days from the first monitoring scan to insemination, followed by a 14-day luteal phase before the pregnancy test, roughly 4 to 6 weeks total. Natural cycle monitoring begins around day 10 to 12.

Does a previous failed IUI cycle reduce the chances of the next one?

Each cycle is statistically independent. There is no evidence that prior failed cycles reduce the probability of the next attempt. Failed cycles do provide clinical information; if protocol issues are identified, your clinic should adjust before repeating.

When should I ask about IVF instead of continuing IUI?

If you are under 38 and have completed three cycles without pregnancy, a review to discuss IVF transition is reasonable. If you are 38 or older, that conversation is appropriate after two to three cycles. You are not required to complete any fixed number of IUI cycles before accessing IVF.

Is IUI abroad covered by insurance?

Most international health insurance plans do not cover fertility treatment at foreign clinics. Many national public health systems, including NHS England, do not fund treatment overseas. Confirm your coverage with your insurer before committing to treatment abroad.