Intrauterine insemination is a procedure in which prepared sperm is introduced directly into the uterine cavity through a thin catheter. It takes a few minutes, requires no anaesthesia, and feels much like a routine gynaecological examination. No egg retrieval. No sedation.
What happens next is entirely up to nature. The sperm make their way towards the fallopian tubes, and if an egg happens to be there at that moment, fertilisation may occur. IUI solves one specific problem: it gets sperm closer to the target by bypassing the cervix and its mucus plug. That's it.
Before the procedure, sperm is 'washed' in the laboratory — centrifuged to separate it from seminal fluid, concentrating the most motile cells. This improves quality compared to what would arrive via intercourse. But the actual fertilisation mechanism is entirely natural.
IUI is often performed alongside mild ovarian stimulation, which increases the number of available eggs from one to two or three, nudging the odds upward. This also introduces a small risk of multiple pregnancy — something that has to be monitored carefully.
IVF isn't simply a more powerful version of IUI. It belongs to a different category of intervention, operating on a different logic altogether. In IVF, eggs are retrieved from the ovaries, fertilised in the laboratory, and the resulting embryo is transferred into the uterus. Everything that IUI leaves to chance — whether sperm and egg will meet, whether fertilisation will occur, whether the embryo will survive — happens under an embryologist's supervision.
That's the real reason IVF success rates are higher. Not because it's 'stronger', but because it eliminates most of the probabilistic losses along the way. Blocked tubes? IVF works around them entirely. Poor sperm motility? ICSI within IVF handles that too. Questions about embryo quality? The embryologist can assess that before transfer.
For IUI, the average pregnancy rate per cycle is around 10 to 20% in women under 35, assuming good sperm parameters, a regular cycle and patent fallopian tubes. After 38, it falls below 10% and continues to decline. Three to six cycles of IUI give a cumulative chance of around 40 to 50% in younger patients.
IVF delivers around 35 to 45% live births per transfer for women under 35. That's per single transfer — not the full cycle including frozen embryos. Cumulative odds across an entire cycle are higher still.
The temptation is to conclude that IVF is always the better bet. But that's a trap. If a 30-year-old woman with patent tubes and a partner with good sperm has a problem only with hostile cervical mucus, three IUI cycles may well do the job without the need for ovarian stimulation, egg retrieval and everything that comes with IVF. A thoughtful clinician will suggest starting with IUI in exactly that scenario.
Intrauterine insemination has fairly specific indications. Cervical factor: mucus that is too thick or contains antisperm antibodies that block sperm movement. Mild male factor: concentration or motility slightly below normal, but not critically so — enough active cells remain after washing. No partner: single women and lesbian couples planning pregnancy with donor sperm make up one of the most common IUI scenarios in Europe. Unexplained infertility at an early stage: when all tests are normal, tubes are patent, sperm is fine, and pregnancy still hasn't happened — IUI with stimulation can be a sensible first move.
One non-negotiable condition for IUI: the fallopian tubes must be open on at least one side. Without that, sperm physically cannot reach the egg, and the procedure is pointless.
Bilateral tubal occlusion is an absolute contraindication to IUI. With this diagnosis, IVF isn't just preferable — it's the only route to biological parenthood using one's own eggs.
Severe male factor infertility. If fewer than one to two million motile sperm remain after washing, IUI offers vanishingly small odds. ICSI within IVF can work with a handful of cells.
Age over 38 to 40. When ovarian reserve is declining, every egg counts. Spending cycles on IUI with its lower success rate means losing time — which is already in short supply. Most specialists in this situation recommend going straight to IVF.
Moderate to severe endometriosis. The inflammatory environment created by endometriosis is toxic to sperm and embryos. IVF allows fertilisation and early embryo development to take place in controlled laboratory conditions — well away from that environment.
Several failed IUI cycles. Three or four unsuccessful IUI cycles in a woman with apparently favourable parameters is a signal to change strategy. Continuing without result serves no clinical purpose.
This deserves a separate mention. Single women and same-sex couples using donor sperm often start with IUI — and that's sensible, provided there are no other indications for IVF. Donor sperm from a bank has already been quality-screened, which improves the starting conditions.
After 35, or with reduced ovarian reserve, the calculation shifts. Even with excellent donor sperm, IUI success rates fall, and moving to IVF becomes increasingly justified.
One IUI cycle at a European clinic averages €300 to €800, not counting donor sperm or stimulation medications. IVF costs €3,000 to €6,000 and above. The difference is real. But if three IUI cycles produce no result and IVF follows, the total expenditure often exceeds what IVF alone would have cost from the start. Clinicians factor this into treatment planning — or they should.
IUI and IVF are not rungs on the same ladder where one inevitably leads to the other. They are different tools for different problems. IUI works where the issue is sperm delivery — not fertilisation itself, or embryo development. IVF takes the entire process under controlled conditions.
The choice is the fertility specialist's to make, with the full clinical picture in front of them. A good specialist won't drag out IUI for unnecessary cycles, and won't rush to IVF without good reason. A sound treatment plan is one where every step is justified.
Cervical factor — a problem with cervical mucus properties that impedes sperm movement. One of the classic indications for IUI.
FET (frozen embryo transfer) — transfer of a previously frozen embryo into a prepared endometrium. Allows use of 'spare' embryos from the same IVF cycle.
ICSI (intracytoplasmic sperm injection) — injection of a single sperm directly into an egg using a microscopic needle. Used for severe male factor infertility within an IVF cycle.
IUI (intrauterine insemination) — introduction of prepared sperm into the uterine cavity via a thin catheter. Fertilisation occurs naturally in the fallopian tube.
IVF (in vitro fertilisation) — fertilisation of an egg with sperm outside the body, followed by transfer of the resulting embryo into the uterus.
Sperm washing — a laboratory procedure separating sperm from seminal fluid and concentrating the most motile cells. Performed before both IUI and IVF.
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