First published [13/10/2026]
The fertilisation rate in IVF is the share of mature eggs that fertilise normally after insemination or ICSI. Many laboratories report roughly 60 to 80 percent in suitable cases, though your own figure can sit above or below that. It is counted from mature eggs, not from every follicle or every egg collected, which is why the same cycle can give different percentages.
Key takeaways
It tells you how many of the eggs that were ready actually showed normal fertilisation. Eggs that were not mature are left out, because they could not be fertilised in the usual way in the first place.
The journey through the laboratory has several steps, and the count can drop at each one:
No single answer fits everyone. As a broad teaching example, many clinics explain that around 60 to 80 percent of mature eggs fertilise normally. Some reports quote an average near 70 percent in selected groups. Treat these as ranges, not promises, and ask your own embryologist what your laboratory sees.
One more thing to keep in mind is that an egg fertilising and an embryo being ready for transfer are different results. The made-up cycle below shows the pattern:
Another patient could see a quite different pattern, and both could be entirely ordinary. For the stages after fertilisation, our day-by-day guide to embryo development shows what happens next.
Because only mature eggs can be fertilised normally. The embryologist first sorts out which eggs have reached the MII stage, and the rate is then discussed against that number. Our guide to IVF egg maturity explains the stages.
The sum looks like this: normally fertilised eggs, divided by mature eggs inseminated or injected, multiplied by 100. A result of “6 of 8” says something different from “6 of 10 retrieved eggs”, so always ask which one the clinic means.
(Normally fertilised eggs ÷ Mature eggs inseminated or injected) × 100
Bring your embryology report to a consultation. Our team will go through each stage with you and explain what it means for your treatment.
Book an IVF consultation →In conventional IVF, prepared sperm and eggs are placed together in a laboratory dish, allowing fertilisation to occur naturally. In ICSI treatment, a single sperm is injected directly into each suitable mature egg.
ICSI may be helpful when sperm have difficulty fertilising an egg, when sperm have been retrieved surgically, or when a previous IVF cycle resulted in poor fertilisation. However, ICSI is not necessary for everyone. Even after injection, an egg must activate and begin dividing. Therefore, ICSI cannot guarantee fertilisation, embryo development, implantation, or a successful pregnancy.
The IVF attrition rate describes how the number of eggs and embryos decreases as they progress through different stages of IVF treatment. Not every follicle contains an egg, not every retrieved egg is mature, and not every fertilised egg develops into a blastocyst.
| IVF Stage | What Can Happen? |
|---|---|
| 1. Egg retrieval | Some follicles may not yield an egg. |
| 2. Egg maturity | Some retrieved eggs may be immature. |
| 3. Fertilisation | Some mature eggs may not fertilise normally. |
| 4. Early embryo development | Some fertilised eggs may stop dividing. |
| 5. Blastocyst development | Some embryos may not reach the blastocyst stage on day 5, 6, or 7. |
| 6. Embryo selection | Embryo assessment or genetic testing, when indicated, may further narrow the options for transfer. |
A smaller number of embryos at a later stage does not automatically mean that an IVF cycle has failed. The significance depends on factors such as age, diagnosis, egg and sperm characteristics, and embryo development.
If none of the eggs fertilise, your fertility specialist and embryologist will review the number of eggs retrieved, their maturity, the trigger medication and timing, the fertilisation method, sperm preparation, and possible egg-activation issues. Previous IVF cycle results may also help identify potential causes.
Read our detailed guide on why IVF eggs fail to fertilise to understand the possible reasons.
Depending on the findings, your doctor may discuss ICSI in a future cycle, adjustments to ovarian stimulation or trigger timing, or further assessment of sperm-related factors. Before choosing an additional treatment or laboratory add-on, ask what specific problem it is intended to address, what evidence supports its use in your situation, and whether it is likely to improve your outcome.
The fertilisation rate is only one stage of the IVF journey. Eggs need to be retrieved, reach maturity, fertilise normally, and continue developing before an embryo may become a blastocyst suitable for transfer or freezing. A meaningful review considers every stage of the process rather than focusing only on the initial egg count.
Learn more about IVF egg retrieval, understand what a blastocyst is, or explore our guide to blastocyst transfer success rates.
Every IVF cycle is different. At Dr. Aravind's IVF Fertility & Pregnancy Centre, you can discuss your results with a fertility specialist and understand the possible next steps. Bring your complete IVF and embryology reports to your consultation.
Book an IVF consultation →Medical Disclaimer: IVF laboratory results and outcomes vary between individuals and clinics. The percentages discussed in this article are general educational ranges and should not be interpreted as a prediction of your individual treatment outcome. Consult a qualified fertility specialist for advice based on your medical history and treatment results.
Many labs see roughly 60 to 80 percent of mature eggs fertilise normally in suitable cases, but no single figure counts as normal for everyone. Your age, the sperm, the method used and the way the lab counts all change the result.
There is no fixed number. A single mature egg can become an embryo, and a larger batch can still end with none that reach blastocyst. Age, sperm, maturity and development all play a part.
No. Fertilization (the American spelling) only says an egg showed normal signs of fertilising. The embryo rate follows how many of those went on to grow, which is a later and lower number.
Not automatically. More eggs give more chances, yet each one still has to be mature, fertilise normally and keep developing.
