What is IUI or Intrauterine Insemination?

Intrauterine insemination (IUI), also called artificial insemination, is a procedure in which concentrated motile sperm are deposited into the uterus through a soft insemination catheter.

Fresh semen is first washed and spun in a test tube to allow the most active sperm to swim through a layer of filtering media. The resulting pellet at the bottom of the tube that contains mainly motile sperm is then resuspended in a special fluid to invigorate the sperm and make them ready for intrauterine insemination (also called IUI or artificial insemination.

Sperm Prep for IUI

IUI pregnancy rates are optimal when at least 3 million motile sperm are available for insemination after semen processing.

Intrauterine insemination can improve the chance of fertilization in 2 ways- by shortening the distance sperm have to swim to meet the egg and by increasing sperm survivability.

Ejaculated sperm are usually a mixture of fast and slow moving sperm. Some sperm are able to move forward and efficiently while others can only wobble, move in circles, or not move at all. Nonmoving sperm can clump together to form a ‘sperm trap’ that can attract motile sperm and impair their ability to get into the uterus.

Sperm washing for IUI recovers sperm that actively swim forward to ensure smooth traffic toward the egg. Millions of motile sperm are placed to the top of the uterus next to the openings into the fallopian tubes. By depositing sperm beyond the cervix and shortening the distance sperm have to travel to meet the egg, artificial insemination improves the odds of fertilization.


Artificial insemination can help improve the chance of pregnancy by prolonging the survival of the sperm by avoiding the vaginal environment.

Normally, the pH of the vagina is slightly acidic to prevent growth of yeast and bacteria and keep it healthy. Unfortunately, sperm dislike an acidic environment and very few of them would survive after an hour in the vagina. In contrast, once in the cervix and the uterus, sperm is can survive for as long as 3-4 days. By avoiding the vaginal route, the IUI procedure can improve the chance of fertilization.

To optimize IUI success, both partners would need to undergo diagnostic evaluation before treatment. Male evaluation usually includes a semen analysis while female evaluation includes a thorough history and physical exam and diagnostic imaging to check the tubes and ovaries.

What Are the Limitations of IUI?

IUI would not be effective in the following situations:


Very Low Sperm Concentration and Motility:

  • In order to get enough motile sperm for IUI, a semen sample usually must have an initial sperm concentration of at least 10 million/ml and progressive motility of at least 15 percent.
  • Semen samples with lower sperm count or motility may not yield enough motile sperm that migrate to the bottom of the tube to create a visible sperm pellet, thus making the IUI procedure impractical.
  • IUI is more successful when there are at least 3 million motile sperm for insemination after processing. The chance of pregnancy with IUI drops significantly when the total motile count is less than 1 million.

Severely Abnormal Sperm Morphology:

  • Sperm with pin head (microcephaly) or round head (globospermia) have been associated with genetic defects and fertilization failure.
  • Sperm with small acrosome region may not have the necessary enzymes to penetrate the shell of the egg for fertilization.
  • With these types of severe sperm morphology, ICSI in an in vitro fertilization cycle can offer a higher chance of success due to the ability to inject the best sperm into the egg to optimize the chance of fertilization.