IUI (intrauterine insemination)

What IUI is

IUI is a short procedure. Sperm are washed and prepared in the laboratory to select the fastest-moving ones, then passed through a thin, soft tube (catheter) via the cervix into the uterus around the time of ovulation. Fertilisation then happens inside the body, as it would after intercourse.

IUI can be done in a natural cycle, without medicines, or in a stimulated cycle, in which tablets or injections help one or two follicles (the small fluid-filled sacs that contain the eggs) to mature.

Who it is generally used for

• Couples with unexplained infertility after a full assessment. NICE (2026) suggests considering up to four cycles of IUI with ovarian stimulation before IVF, or moving straight to IVF; ESHRE (2023) recommends IUI with ovarian stimulation as a first-line option; WHO (2025) suggests a period of trying naturally first, then IUI with clomifene or letrozole tablets, and rates the certainty of this evidence as low.
• Women with mild endometriosis and open fallopian tubes, as one of the options NICE lists alongside IVF
• Couples for whom vaginal intercourse is not possible or is very difficult, because of a physical disability or a psychosexual problem

IUI needs open fallopian tubes and sperm that can be prepared in sufficient numbers, so the tubes are usually checked before treatment. When the tubes are blocked or the sperm count is very low, IUI is not an alternative to IVF or ICSI.

How a cycle works

Monitoring. In a stimulated cycle, medicines encourage one or two follicles to grow, and vaginal ultrasound scans follow their growth. Guidelines advise ultrasound monitoring when hormone injections (gonadotrophins) are used, to reduce the risk of multiple pregnancy and ovarian hyperstimulation, and the HFEA advises that treatment should be stopped if too many follicles develop.

Timing. When a follicle is ready, a hormone injection is often given to trigger the release of the egg, and the insemination is timed around it.

The procedure. On the day, the sperm sample is washed and prepared. A speculum is placed in the vagina, and the prepared sperm are passed into the uterus through a thin catheter. It usually takes no more than about ten minutes. It can be uncomfortable, and there may be some cramping for a short time afterwards; most people go home after a short rest.

Afterwards. You are told when to take a pregnancy test. How many cycles to try before reviewing the plan is usually agreed in advance; WHO notes that the optimal number of stimulated cycles is not known, and that studies have used between one and six.