Patients often see "IVF" and "ICSI" listed side by side on a price sheet and assume they are alternatives you choose between, like two different procedures. In fact, the UK regulator describes ICSI as a treatment carried out as part of IVF, with the rest of the process unchanged (HFEA). This article compares the two side by side so you can see exactly where they differ and what that means for you. For a deeper look at the evidence behind ICSI's uses, see our separate guide, ICSI: what it is and when it is actually needed.
Side by side
| Conventional IVF | ICSI | |
|---|---|---|
| How sperm meet the egg | Prepared sperm are placed with each egg in culture; one sperm must enter by itself | An embryologist injects a single sperm directly into each egg |
| Preparation of eggs | Eggs stay in their surrounding cells | Surrounding cells are removed so the egg can be assessed and injected |
| Which eggs can be used | All collected eggs are exposed to sperm | Only eggs judged mature enough are injected |
| Sperm needed | Enough moving sperm to find and enter the eggs | Very few sperm, including surgically retrieved sperm |
| Main uses | Many causes of infertility where sperm are adequate | Sperm problems, previous fertilisation failure, some genetic testing |
| Cost | Base IVF price | Usually an extra charge |
| Everything else | Stimulation, collection, embryo culture, freezing and transfer are the same | |
What actually happens on collection day
With conventional IVF
The partner's or donor's sperm sample is washed and concentrated in the lab. Each egg, still wrapped in its cloud of support cells, is placed with a measured number of moving sperm. The sperm have to work through those cells and the egg's outer shell on their own, as they would in the body. The lab leaves them together and checks for signs of fertilisation the next morning.
With ICSI
The egg's support cells are gently removed, which lets the embryologist see whether each egg is mature. Under a microscope, a fine glass needle picks up one sperm and injects it into the centre of each mature egg. The eggs then go into culture and are checked the next morning, just as with conventional IVF.
The NHS describes the clinic calling the day after fertilisation with the number of embryos (NHS, reviewed 2025). That call is when the two methods produce slightly different reports.
How the fertilisation report differs
Your day-1 report is easier to read if you know which number is the starting point:
- Conventional IVF: the lab often does not know how many eggs were mature until the next day, because the support cells hid them. The report may say how many eggs fertilised out of all eggs collected.
- ICSI: the lab knows on collection day how many eggs were mature and injected. The report usually says how many fertilised out of those injected. Immature eggs are not injected, so the count can look smaller than the number collected.
When comparing your result with anything you read online, check whether the percentage is out of all eggs or out of mature eggs. They are different numbers, and mixing them up causes a lot of needless worry.
An illustration of reading the report
Illustrative example, not real data: suppose ten eggs are collected. With ICSI, the lab finds eight mature, injects those eight, and six fertilise. The report might read "6 of 8 injected", which sounds like 75%. With conventional IVF on a similar set of eggs, the report might read "6 of 10 collected", which sounds like 60%. The embryos are the same number in both cases; only the starting point changed. If you ever compare your report with a friend's, or with a figure online, line up the starting points first.
Who is usually offered ICSI
The UK regulator lists situations where a doctor may suggest ICSI (HFEA):
- A very low sperm count
- Sperm with abnormal shape or poor movement
- A previous IVF cycle where no eggs, or very few, fertilised
- Sperm that have to be collected surgically
- Poor-quality frozen sperm
- Planned embryo genetic testing, where stray sperm stuck to the outside of an egg could affect results
The regulator also notes that around half of heterosexual couples with fertility problems have a sperm-related cause, which is one reason ICSI is so widely used. How the sample is processed before either method matters too; our guide to sperm preparation for IVF and ICSI explains washing and total motile count.
When ICSI is unlikely to add anything
If sperm results are normal and there is no history of fertilisation problems, ICSI's case is much weaker. The UK regulator states that there is currently no scientific evidence supporting ICSI where infertility is not related to sperm, and that UK and European professional guidance does not recommend it over standard IVF in those cases. It adds that choosing ICSI when it is not needed may raise costs without clear evidence of better results (HFEA).
ICSI is also not a fix for every fertilisation problem. The same source says it is unlikely to help if earlier poor fertilisation was caused by poor-quality or immature eggs. If fertilisation has failed before, it is worth understanding why before assuming ICSI is the answer; our article on fertilisation failure after IVF covers that review.
Risks: what is the same and what is different
Both methods share the usual IVF risks, such as ovarian hyperstimulation and multiple pregnancy. For ICSI specifically, the UK regulator mentions (HFEA):
- A slightly higher risk overall, including possible damage to eggs during cleaning and injection
- A suggested but unproven link to long-term child health issues, and genetic or developmental problems seen in a very small number of children, which may stem from the underlying infertility rather than the procedure
- The possibility that a son conceived by ICSI inherits his father's or donor's infertility, which is highly likely where a clear genetic cause exists
Where severe male infertility may have a genetic cause, the regulator suggests considering genetic testing beforehand, ideally after talking it through with a counsellor.
Who decides, and when
In most clinics the fertilisation method is set before stimulation, based on semen analysis and history. It can change on the day: for example, a clinic may switch to ICSI if the fresh sample is much poorer than expected. Ask now so you are not surprised:
- Which method are you planning for us, and what in our results points to it?
- Would you ever change the method on collection day, and would you ask us first?
- Is ICSI included in my quote or an extra charge?
- Do you ever split the eggs between the two methods, and when?
- Will my fertilisation report be out of all eggs or out of mature eggs?
The Takeaway
Think of ICSI as a lab tool inside IVF rather than a separate treatment. It is valuable when sperm need help or fertilisation has failed before, and offers no proven gain otherwise. Ask your clinic to tie its choice to your own results.
Frequently asked questions
Does ICSI change what I go through physically?
No. Medications, scans, egg collection and transfer are the same. The only difference happens in the lab after your eggs are collected.
Are success rates different between IVF and ICSI?
The UK regulator says ICSI success rates are very similar to IVF's. The method is chosen to solve a specific problem, not to boost odds in general.
Can we choose ICSI just to be safe?
You can ask, but without a sperm-related reason there is no evidence it helps, and it usually costs more. Ask your clinic to explain its reasoning in your case.
We are using donor sperm. Do we need ICSI?
Not automatically. Donor samples are often of good quality, so conventional IVF may be fine, but frozen sperm quality varies and some clinics have their own policies. Ask what your sample's results show.
Why were fewer of my eggs used with ICSI?
Only mature eggs can be injected. Immature eggs collected on the day are usually set aside, which is why the injected number can be lower than the number collected.