Intrauterine insemination (IUI)

A simple and effective treatment to achieve pregnancy

Intrauterine insemination (IUI) is an assisted reproduction technique indicated in cases of mild infertility. It consists of placing a prepared semen sample inside the uterus at the time of ovulation, in order to facilitate the meeting between egg and sperm. It is a quick, painless procedure with good results, especially recommended for young women and couples facing initial reproductive difficulties.
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What is IUI?

Intrauterine insemination (IUI), also known as "artificial insemination", consists of placing sperm inside the woman’s uterus to facilitate fertilisation. The goal is to increase the number of sperm reaching the fallopian tubes and thereby improve the chances of fertilisation.

IUI is a fertility treatment in which high-quality sperm are selected, separating them from those that are less optimal or have poor motility. It is a method commonly used by people who use donor sperm in their treatment, including single women and female couples, although it can also be a suitable option for some heterosexual couples.

Who can undergo IUI?

People choose intrauterine insemination (IUI) for various reasons, such as fertility problems, or as a reproductive option for female couples or single women who wish to have a baby using donor sperm.
IUI may be a suitable option in the following cases:

Problems with cervical mucus or other cervix-related issues
The cervix connects the vagina to the uterus. Cervical mucus helps sperm move towards the fallopian tubes, but if it is too thick, it can hinder their movement. With IUI, the sperm are placed directly into the uterus, bypassing the cervix.
A semen analysis may show that the sperm are few in number, have low motility, abnormal shape, or are weak. IUI makes it possible to select and use only the highest-quality sperm for the treatment.
IUI is used when sperm from someone other than the gestational partner is required. This is known as donor insemination (DI) and is performed when one partner does not produce sperm or the quality is too low. It is also an option for single women or female couples.
IUI can be helpful when one partner has difficulty achieving or maintaining an erection, or is unable to ejaculate.
In rare cases, a person may be allergic to their partner’s semen, which causes vaginal irritation, burning, or redness. IUI can help, since during the “sperm washing” process the proteins that trigger the allergy are removed.
IUI can also be used when no specific cause of infertility has been identified, as part of an initial treatment.

How does IUI work?

Before starting artificial insemination treatment, a personalised evaluation of the couple or single woman is carried out to determine the most appropriate procedure in each case.
After the initial assessment, a full gynaecological examination is performed to evaluate the condition of the uterus, fallopian tubes, and the woman’s ovarian reserve, as well as a hormonal analysis. If a couple attends the clinic, the man will also undergo a fertility study through semen analysis.
Intrauterine insemination (IUI) involves some key steps before the procedure itself:

Ovulation

The timing of ovulation is essential to ensure that the sperm is injected at the right moment.
To get the timing right, you can use an at-home urine ovulation predictor kit. This kit detects when your body produces a surge in luteinising hormone (LH), which triggers the ovary to release an egg. Alternatively, you could have a transvaginal ultrasound, which produces images of your ovaries and the growth of the eggs. You may also be given an injection of human chorionic gonadotropin (hCG) or other medication to stimulate the release of one or more eggs at the right time.

Preparation of the semen sample

Your partner provides a fresh sperm sample on the same day as the IUI procedure. In some cases, it can be provided in advance and your healthcare professional may freeze it until it is needed. If you are using donor sperm, the sample is thawed and prepared.

The sperm is prepared for insemination through a process called “sperm washing”, which concentrates the number of healthy sperm. If you are using donor sperm, the sperm bank usually provides the sample already washed.

Inseminación

El procedimiento de inseminación es sencillo y dura solo unos minutos. Te recostarás en la camilla de exploración y tu profesional de salud insertará un espéculo en tu vagina, similar a lo que ocurre durante una prueba de Papanicolau. Luego, se introduce suavemente un catéter a través del cuello uterino hasta el útero. Finalmente, el profesional inyecta la muestra de esperma lavada en el útero. 

After the IUI procedure

  • You may be asked to remain lying down for 10 to 30 minutes after the insemination. Pregnancy occurs if a sperm fertilises an egg and the fertilised egg implants in the lining of your uterus.
  • You may be given progesterone after IUI. Progesterone helps maintain the lining of the uterus and can improve the chances of implantation.
  • You can take a pregnancy test about two weeks after the IUI.

What to know before starting IUI treatment

Before starting IUI treatment, you will need a full medical examination and fertility tests. Your partner will also be examined and tested.
The tests and examinations prior to IUI treatment may include:

  • Ultrasounds of the uterus
  • Semen analysis
  • Screening tests for sexually transmitted infections (STIs) and other infectious diseases
  • Blood tests
  • Your healthcare professional may recommend taking folic acid (found in most prenatal vitamins) at least three months before conception (or before IUI treatment).

Success rates of IUI

The effectiveness of IUI depends largely on the underlying cause of infertility and the age of the person conceiving.
The fertility rate with IUI is comparable to that of natural conception (around 20%), which means that IUI helps many people achieve a success rate closer to the natural average.

The success rates of intrauterine insemination (IUI) range between 7% and 10% per cycle if you have two functional fallopian tubes and healthy, good-quality sperm.

10 %

When fertility medication is used, the pregnancy rate can increase to up to 20% per cycle.

20 %

Frequently asked questions about IUI

What can I expect after intrauterine insemination (IUI) treatment?

Most people can return to their normal daily activities immediately. You should avoid any activity that causes discomfort after the procedure, but in general there are no major restrictions.

When can I take a pregnancy test after IUI?

You can take a pregnancy test about two weeks after the treatment.

How painful is IUI treatment?

Intrauterine insemination does not require anaesthesia and generally should not be painful. However, you may feel mild cramping or discomfort during and just after the procedure.

What medications are used during IUI?

IUI is often combined with fertility medication that stimulates your ovaries to produce and release as many eggs as possible. However, they are not always necessary; your doctor will explain whether their use is recommended in your particular case.

What are the risks of IUI?

IUI is a low-risk fertility treatment, especially compared with more invasive options such as in vitro fertilisation (IVF).

How many rounds of IUI should I try before moving on to IVF?

The optimal number of intrauterine insemination attempts before considering in vitro fertilisation varies from person to person.
In general, specialists recommend between 3 and 6 IUI cycles before rethinking the treatment plan.
Factors such as age, specific causes of infertility, previous results, and your personal preferences all influence this decision.
If IUI is not successful after several attempts, or if there are particular challenges to achieving pregnancy, IVF may represent a more direct and effective path.
Your doctor will guide you according to your specific situation.

Do I need rest after IUI treatment?

Absolute rest is not necessary. Many people resume their normal activities the same day. It is recommended to avoid strenuous activities for a few hours, but there are no strict instructions for rest.

Sí. La IIU es una opción accesible y efectiva para parejas del mismo sexo, mujeres solteras o cualquier persona que necesite recurrir a donación de esperma para lograr un embarazo.

Yes. IUI is an accessible and effective option for same-sex couples, single women, or anyone who needs to use donor sperm to achieve pregnancy.

How long does the IUI procedure take?

The procedure itself is quick and simple, usually lasting between 10 and 15 minutes. It does not require hospitalisation or anaesthesia.

Is ovarian stimulation necessary for IUI?

Not always. In some cases, IUI is performed in a natural cycle, meaning without medication. However, medication is often used to improve the chances of success. The doctor will decide what is most appropriate in your situation.

What happens if IUI is not successful?

If pregnancy does not occur after several attempts, the doctor will evaluate other options such as changes in medication, further tests, or moving on to techniques like IVF. The goal is to find the most suitable path according to your needs.

¿Cuáles son los requisitos para considerar una IIU como opción viable?

Se recomienda cuando las trompas están permeables (al menos una), la calidad del semen es adecuada (mínimo ~3‑5 millones de espermatozoides móviles tras capacitación) y la pareja tiene buen pronóstico reproductivo general. La IIU es especialmente útil en casos de infertilidad inexplicada, factor masculino leve, problemas del moco cervical o mujeres sin pareja masculina.

¿En qué momento exacto se realiza la IIU respecto a la ovulación?

La inseminación se realiza entre 32 y 36 horas después de la administración de hCG, la cual se utiliza para inducir la ovulación cuando el folículo está maduro.

¿Qué significa “capacitación del semen” y por qué es importante?

Se trata de un proceso de laboratorio donde se seleccionan los espermatozoides de mejor calidad (movilidad y morfología), mediante lavado y gradientes de densidad, para depositarlos en el útero y maximizar las posibilidades de fecundación.

¿Cuántos ciclos de IIU se recomiendan antes de pasar a FIV?

Si no hay embarazo tras 3 a 6 ciclos, se suele recomendar considerar técnicas más avanzadas como la FIV. La probabilidad de éxito descarta mayores beneficios tras el quinto ciclo si no se obtiene resultado.

¿Es la IIU realmente segura? ¿Cuáles son los principales riesgos?

Es un procedimiento seguro y mínimamente invasivo, con molestias leves en ocasiones (tipo cólico) y un riesgo muy bajo de complicaciones. La única situación de mayor cautela es el riesgo aumentado de embarazo múltiple si se usan medicamentos para estimular la ovulación.

¿Qué papel tiene el soporte de fase lutea en la IIU?

Aunque el cuerpo lo produce de forma natural, se suele administrar progesterona como soporte durante la fase lútea para mejorar la implantación del embrión.

¿Qué diferencias hay entre una IIU en ciclo natural y una con estimulación?

  • Ciclo natural: la ovulación ocurre espontáneamente; la inseminación se programa en consecuencia.

  • Ciclo estimulado: se usan medicación (como clomifeno o gonadotropinas) para aumentar el número de folículos y, por tanto, la probabilidad de éxito.