ICSI Explained: What Intracytoplasmic Sperm Injection Is and When It Is Used

ICSI (intracytoplasmic sperm injection) is a laboratory technique used during IVF in which an embryologist injects a single sperm directly into each egg, instead of leaving eggs and sperm to fertilise on their own. It changes only one step of treatment, the fertilisation step, and is used mainly when sperm is the difficulty. When our consultant first said the word, I assumed it was a different treatment altogether; in truth it sits inside an ordinary IVF cycle.

What ICSI is

ICSI is a way of fertilising an egg by injecting one chosen sperm into it under a microscope. The embryologist holds a mature egg still and uses a fine glass needle to place a single sperm into the centre of the egg, then watches over the next day to see whether it has fertilised normally. Because only one sperm is needed per egg, ICSI can work even when very few healthy sperm are available. It was first used successfully in the early 1990s and is now one of the most common fertilisation methods in assisted conception worldwide.

When ICSI is used

ICSI is used mainly for male factor infertility, which is a factor in roughly half of couples who struggle to conceive. Clinics typically offer it when a semen analysis shows a low sperm count, sperm that move poorly, or sperm with an abnormal shape, and when sperm has been retrieved surgically from the testicles because there is none in the ejaculate. It is also used when a previous standard IVF cycle had unexpectedly low or no fertilisation, even with normal-looking sperm. The decision rests on the semen results and your history, explained in our guide to male factor infertility. Where sperm is normal, guidance from bodies such as the HFEA is that ICSI should not be added routinely, because it does not improve the outcome.

How ICSI differs from conventional IVF

The only difference between ICSI and standard IVF is how the egg meets the sperm in the lab. In conventional IVF, the collected eggs and a prepared sperm sample are placed together in a dish, and fertilisation happens when a sperm reaches and enters an egg on its own, much as it would in the body. In ICSI, the embryologist selects one sperm and injects it directly into each mature egg, doing the work that the sperm could not do unaided. For you as a patient the experience is identical: the same two weeks or so of stimulation injections, the same egg collection under sedation, the same embryo transfer, and the same two-week wait afterwards. The extra work is the embryologist’s, not yours.

How well ICSI works

ICSI raises the chance that eggs fertilise when sperm quality is the obstacle, which is precisely the situation it is designed for. What it does not do, on the current evidence, is produce higher live-birth rates than standard IVF when sperm is normal, which is why it is not worth paying for as a default extra. As with all assisted conception, the strongest predictor of success is the woman’s age, with chances per cycle highest under about 35 and declining more steeply from the late 30s. Always check what any quoted figure counts: per cycle started or per transfer, and pregnancy or live birth, since live birth is lower and the one that matters. We unpack this fully in IVF success rates.

Risks and what to ask

ICSI carries the same risks as any IVF cycle, including ovarian hyperstimulation syndrome (OHSS) and a higher chance of multiple pregnancy if more than one embryo is transferred. Because ICSI bypasses the natural selection of sperm, regulators note a small possible increase in certain birth differences; much of this is thought to relate to the underlying fertility problem rather than the technique itself, and your clinic will talk it through before you consent. ICSI is also usually an added cost on top of IVF, so ask for an itemised quote and compare it against our guide on how much IVF costs.

If a clinic suggests ICSI, it is reasonable to ask why it is being recommended for you specifically, what your semen analysis showed, and whether it is likely to change your chance of a baby. A good team will welcome the question.

This guide is general information and support, not a diagnosis or individual medical advice. If you have concerns about fertility, do not delay: speak to your GP or a fertility specialist, who can advise on the right approach for you.