Fertilization failure after IVF: what it means and what clinics may change next

The morning after egg collection, the lab checks which eggs have fertilised and calls you with the result. Most people are braced for a number smaller than their egg count. Fewer are ready for a call saying that very few eggs fertilised, or none did.

If that has happened to you, it is a hard moment. It is also, usually, an informative one. Fertilisation is a specific biological event with identifiable steps, and when it fails, there are concrete questions a clinic can ask about which step went wrong and what to do differently next time.

What "fertilisation failure" actually describes

Clinics use the phrase for two different situations:

• Total fertilisation failure: none of the mature eggs fertilised.
• Low fertilisation: some eggs fertilised, but noticeably fewer than expected for the number of mature eggs available.

There is no agreed threshold for "low." The ASRM Practice Committee's 2026 opinion on ICSI notes that no established cutoff defines it. In practice, the clinic judges your result against how many eggs were mature, which method was used, and what the sperm looked like on the day.

The starting count matters. One fertilised egg out of two mature eggs is a very different event from one out of twelve, even though both produce "one embryo." Always ask for the number of mature eggs alongside the number that fertilised.

The steps where fertilisation can break down

For an egg to fertilise, several things must go right in sequence. Thinking about them one at a time makes the conversation with your clinic far more productive.

The embryology notes are often more useful than the diagnosis on your file. A label like "unexplained infertility" says little. A note that most eggs were immature, or that sperm did not bind, points somewhere specific. Our guides to egg maturity reports and sperm preparation for IVF and ICSI explain what those notes mean.

A normal semen analysis is not the whole story

A routine semen analysis measures how many sperm there are, how well they move, and their shape. Fertilisation depends on what sperm can do when they meet an egg, which a standard test does not fully capture. A normal result makes a sperm problem less likely but does not rule out a functional one.

After conventional IVF fails: what the evidence says about ICSI

If the failed cycle used conventional insemination (eggs and sperm placed together in a dish), the most common next step is ICSI, where an embryologist injects a single sperm directly into each mature egg.

ASRM's 2026 opinion supports this. It says ICSI can increase fertilisation in a later cycle after lower-than-expected or failed fertilisation with conventional insemination. In one prospective study it describes, eggs from patients with this history fertilised at a rate of 62.9% with ICSI (90 of 143 eggs) compared with 0% with conventional insemination (0 of 89).

The same document is equally clear about the limits of ICSI when there has been no failure and no male-factor problem:

• Routine ICSI for non-male-factor infertility is not recommended.
• Large randomised trials it reviews did not show more live births with routine ICSI. A 2021 trial of 1,064 couples with normal sperm count and motility reported live birth rates of 32.7% with conventional IVF and 33.6% with ICSI.
• In a 415-couple trial, total fertilisation failure happened in 5% of conventional cycles and 2% of ICSI cycles, meaning about 33 couples would need ICSI to prevent one failure.

Put simply, total failure with conventional IVF is not common, and ICSI for everyone does not raise birth rates. But once you have actually experienced low or failed fertilisation, the balance shifts and ICSI becomes a reasonable change to discuss. For a broader view of when ICSI is used, see ICSI: what it is and when it's needed.

Splitting the eggs

Some clinics suggest a "split" approach in the next cycle: some eggs are inseminated conventionally and the rest by ICSI. ASRM's opinion refers to "sibling oocyte" studies that compare the two methods on eggs from the same patient. A split can show whether your eggs fertilise by both routes, which can be useful information for any future cycle. Whether it suits you depends on how many eggs you expect.

When fertilisation fails even with ICSI

Failure after ICSI raises a different set of questions, because ICSI already bypasses the step of sperm reaching and entering the egg. Attention then moves to:

• Egg activation. In some cases the egg does not respond after sperm is injected. The UK regulator notes that artificial egg activation using calcium ionophore was taken off its add-ons rating list in October 2023 and is now an authorised process for selected patients only (HFEA, reviewed 2026). Ask whether you would be considered a suitable candidate, and on what evidence.
• Egg maturity and quality. If many eggs were immature, the trigger type or timing may be reviewed.
• Specialist sperm testing. A referral to an andrologist or reproductive urologist may be suggested.
• Rare genetic causes. Repeated, unexplained total failure sometimes leads to genetic counselling for one or both partners.

Donor eggs or donor sperm may eventually come up. That conversation should follow a clear review of which gamete is actually suspected, not replace it.

What a clinic may change for the next cycle

• The fertilisation method (conventional, ICSI, or a split)
• The trigger medication or its timing, if many eggs were immature
• Sperm preparation, or the sperm source used (for example, a fresh rather than frozen sample)
• Further testing of the male partner, or of the eggs' response, before stimulation starts
• Activation techniques, only where the history clearly supports them

It is just as valid for the clinic to say that nothing obvious went wrong and the same approach is worth repeating. A single cycle of low fertilisation does not always mean it will happen again.

In the first few days after the call

You do not have to decide anything on the day you hear the result. It is reasonable to ask for a follow-up appointment once the full lab report is ready, rather than trying to absorb everything on a short phone call. Write down your questions as they come up. If you have a partner, decide together who will ask what, so neither of you has to carry the whole conversation. Many people also find it helps to talk to a counsellor who understands fertility treatment before planning the next step.

Questions to ask after a low-fertilisation result

• How many eggs were mature, and how many of those fertilised?
• Which method did you use, and why?
• What were the sperm count and motility after preparation on the day?
• Did the embryologist see anything unusual in the eggs or in how sperm behaved?
• Would you change the method, the trigger, or the sperm preparation next time?
• Is egg activation failure suspected? If so, what is the evidence?

If your next cycle will be at a different clinic or abroad

Ask the first clinic for the full embryology report, not just a summary letter. It should list mature eggs, the insemination method, fertilisation per egg, and any lab notes. A new team can only build on what it can see, and these details are hard to recover later.

Frequently asked questions