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What is IUI and how does it work?

What is IUI and how does it work?
What is IUI and how does it work?

What is IUI and how does it work? In this short post, Dr Janet Evans, Consultant Gynaecologist and Fertility Specialist at our LWC Cardiff clinic explains what you need to know.

What is IUI?

Intrauterine insemination is a treatment where prepared sperms are introduced into the woman’s uterine cavity on the day of ovulation, in order to improve the chances of conception.

How does it work?

The treatment can be thought of as a less invasive, simpler form of IVF. This involves:

  • Stimulating, or just monitoring, the growth and release of the egg
  • Then on the day of ovulation, separating the sperms from the semen and mixing them with sterile culture medium, to avoid any germs
  • Passing a soft plastic tube through the cervix (the neck of the womb) in a process like a cervical smear, and injecting the sperms through this into the uterus, so that they can swim up the fallopian tubes to find and fertilise the recently released eggs.

What is Stimulated IUI?

In humans, not all eggs are fertile, and treatment using natural ovulation and therefore only one egg, will have a pregnancy rate of around 1 in 5, and this will reduce with age, a bit like throwing dice to get a 6.

To increase pregnancy success rates, the ovaries can be stimulated with tablets or injections to produce several eggs (similar to having several throws of the dice.) This will increase the chances of a good quality egg and, with some techniques, will also control the timing of ovulation. It can also increase the chances of multiple pregnancies, which is not always as safe for mum or baby as a single baby.

Who needs IUI?

The treatment may be useful in several situations


  • The woman needs to be still ovulating - i.e. not menopausal
  • The sperm count should be normal
  • The Fallopian tubes need to be open to allow sperms and eggs to meet

What are the advantages and disadvantages of IUI compared to IVF?

IVF is a process where eggs are removed surgically from the ovaries and mixed with sperm in the laboratory. The resulting embryos are grown in the laboratory for around five days, and then an embryo is placed into the womb. Any other good quality embryos are vitrified and stored for future use.

IVF is a more invasive, technologically challenging, and expensive treatment compared to IUI, but it's advantages are those of a better pregnancy rate and the possibility of being able to return for stored embryos rather than starting again.

For some couples also, IVF will be needed because the Fallopian tubes are blocked or the sperms may be too weak to be able to fertilise eggs naturally, making IUI inappropriate.

How can the London Women’s Clinic help?

If you are considering IUI, you will need a consultation to discuss options and explore your reasons for opting for IUI

  • We can provide a full service of sperm preparation, - either partner or donor and work closely with our sister organisation – the London Sperm Bank to offer a range of donors.
  • We can undertake the work up to investigate your ovarian function, tubal patency and semen analysis if appropriate, together with the standard pre treatment testing of full blood count, rubella, HIV, Hep B&C, chlamydia.
  • We can advise you about stimulation and monitor your response with a daily scanning service.
  • Our laboratories which are consistently providing some of the best IVF pregnancy rates in Wales and the West of England will give you the best chance of pregnancy with IUI.
  • Should you wish at some point to change from IUI to IVF, this can be managed seamlessly, without change of clinic.


Please note, as success rates for IUI in women over 40 years of age tend to be very low, due to biological factors, we feel that it would be unethical to offer IUI treatment in this situation and would always recommend IVF.

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