Semen Preparation for IUI: Density Gradient vs Swim-Up Explained

A well-timed insemination is only as good as the sample that is inseminated. For gynaecologists offering IUI, understanding semen preparation helps with choosing the right method, reading the lab report and counselling couples realistically.

Key takeaways

• Raw semen must never be placed in the uterus; preparation removes seminal plasma, debris and non-motile sperm.
• Density gradient centrifugation suits poorer samples, while swim-up suits samples with good concentration and motility.
• The post-wash total motile sperm count helps clinicians counsel couples about IUI versus IVF or ICSI.
• In India, donor semen must come from a registered ART bank, and IUI must be performed in a registered ART clinic.

Why semen must be prepared

Raw semen cannot be placed directly into the uterus. Preparation:

• Removes seminal plasma, which contains prostaglandins that can cause painful uterine cramps
• Removes dead sperm, debris, white cells and bacteria
• Concentrates motile sperm in a small volume of culture medium
• Allows the sperm to begin capacitation

The WHO laboratory manual (6th edition) describes the standard methods.

Density gradient centrifugation

The sample is layered over two layers of a colloidal solution with different densities and centrifuged. Motile, morphologically normal sperm pass through the layers and collect in a pellet at the bottom, which is then washed and resuspended.

Best suited for:

• Samples with low concentration or motility
• Samples with a lot of debris or cells
• Routine use in many IUI and IVF laboratories

Swim-up

The washed sample or pellet is covered with culture medium, and motile sperm swim up into the medium over a period of incubation. The top layer is collected for insemination.

Best suited for:

• Samples with good concentration and motility
• Laboratories wanting a simple, gentle method

The yield can be lower than with density gradients when the sample is poor.

Simple washing

Simple dilution and centrifugation removes seminal plasma but does not select motile sperm, so it is less commonly used on its own for IUI.

Reading the post-wash report

The key number for IUI is the total motile sperm count after preparation. Many clinics use a threshold when counselling couples, because very low counts are associated with lower chances of success with IUI and may point towards IVF or ICSI instead. Thresholds vary between studies and clinics, so local data and the full clinical picture should guide decisions.

Quality points for every IUI clinic

• Clear collection instructions, including the abstinence period and a sterile, non-toxic container
• Processing within the recommended time after collection
• Double-checking patient identity at collection, processing and insemination
• Sterile technique and quality-controlled media
• Insemination soon after preparation

Donor semen and the law in India

Under the ART (Regulation) Act 2021, IUI is performed in registered ART clinics, and donor semen may only be obtained through a registered ART bank, with the consents the Act requires. Clinics should keep records of every insemination.

Frequently asked questions

Which method gives better IUI results?

Studies have not shown a consistent difference between density gradient and swim-up for IUI outcomes. The choice is usually based on sample quality and laboratory practice.

How long can a prepared sample wait before insemination?

It is best to inseminate soon after preparation and within the time your laboratory protocol allows.

Can a gynaecologist learn semen preparation?

Yes. With hands-on training and quality control, clinicians and their staff can run a reliable IUI laboratory.

Learn IUI semen preparation at ReproNest

ReproNest's IUI Training Course includes hands-on semen preparation, counting chambers and insemination technique on training models, along with guidance on setting up a registered IUI service. Read our step-by-step IUI guide, or contact us.

This article is educational content for healthcare professionals and trainees. It is not medical advice and does not replace clinical judgement, current guidelines or the ART (Regulation) Act 2021 and Rules 2022.