Sperm Selection for ICSI: Morphology, Motility and When Advanced Methods Help

In ICSI, the embryologist chooses a single sperm for each oocyte. That choice, and how the sperm is prepared and immobilised, is a hands-on skill that every ICSI trainee must master. It is also an area where many "advanced" selection techniques are marketed, so knowing the evidence matters.

Key takeaways

• Standard ICSI selects a motile sperm with normal-looking morphology under high magnification on the inverted microscope.
• The sperm is immobilised by gently compressing its tail before injection.
• For immotile samples, viability tests help identify live sperm before injection.
• ESHRE does not recommend routine use of IMSI, PICSI or other selection add-ons, as benefit on live birth is not established.

Preparing the injection dish

Sperm are usually placed in a viscous medium, most often polyvinylpyrrolidone (PVP), which slows them down so they can be picked up. Oocytes sit in separate droplets of handling medium, and the dish is kept at the correct temperature on a heated stage.

Choosing the sperm

The embryologist looks for a sperm that:

• Is progressively motile, or at least moving
• Has a normal-looking head shape, without large vacuoles visible at standard magnification
• Has an intact midpiece and tail

The aim is a reasonable, quick choice, not an exhaustive search. Long searches keep oocytes out of optimal conditions.

Immobilising the sperm

Before aspiration, the sperm's tail is gently compressed with the injection pipette against the dish. This stops movement and is thought to help activation after injection. The sperm is then drawn into the pipette tail-first.

Handling immotile samples

When no motile sperm are present, for example in some testicular samples, embryologists need to tell live sperm from dead ones. Options include:

• The hypo-osmotic swelling (HOS) test, where live sperm tails curl
• Laser-assisted identification of live sperm in some laboratories

These help avoid injecting non-viable sperm.

What about advanced selection methods?

Several add-ons claim to select "better" sperm:

• IMSI: very high magnification to look for vacuoles
• PICSI: selection by binding to hyaluronan
• Microfluidic sorting and other devices

ESHRE's good practice recommendations on IVF add-ons do not recommend these for routine use, because trials have not shown a clear improvement in live birth rates. Patients should receive balanced information before any add-on is offered.

Measuring ICSI quality

Laboratories track ICSI performance with indicators such as the normal fertilisation rate and the oocyte degeneration rate, comparing them with published consensus reference values and their own history. A rise in degeneration can point to technique, pipette or handling problems, and should prompt a review of each embryologist's results and refresher training where needed.

Practice before clinical work

Sperm selection and immobilisation are learned at the micromanipulator through repeated practice on training material. Trainees should be signed off by a senior embryologist before injecting clinical oocytes.

Frequently asked questions

Does sperm morphology on the semen report affect ICSI?

ICSI bypasses many sperm problems, so a low morphology score on the semen report does not by itself prevent successful fertilisation with ICSI.

Is PVP harmful to the embryo?

PVP is widely used in ICSI. Good practice is to inject as little of it as possible along with the sperm.

Can testicular sperm be used for ICSI?

Yes. Surgically retrieved sperm are commonly used for ICSI in men with azoospermia, under specialist care.

Learn ICSI sperm handling at ReproNest

ReproNest's Advanced ICSI & Micromanipulation Course includes one-to-one practice in sperm selection, immobilisation and injection on training material. Read about ICSI versus conventional IVF, 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.