IVF Attrition Rate: Why Don’t All Eggs Create Embryos?

You're finally ready to take the next big step on your IVF journey: egg retrieval and embryo creation! This is an exciting stage, but can also feel disheartening, as you receive daily reports of your dwindling egg or embryo count. Is this normal? And what is IVF attrition rate?

Skip to a section:

• Common Questions About IVF
• What is IVF attrition rate?
• IVF by the Numbers: Attrition Rate Example
• Phase 1: Egg Retrieval
• Phase 2: Fertilization
• Phase 3: Embryo Growth & Development
• Why don't all eggs create healthy embryos?
• What will my personal IVF attrition rate be?
• The Bottom Line: Attrition is Normal

Common Questions About IVF 

As a physician at Illume Fertility, my number one goal is to help hopeful parents-to-be grow their families. It's only natural to come in with questions, concerns, and an understandable amount of anxiety. Seeking the help of a fertility specialist takes courage, and we respect each patient who reaches out to us for taking that leap!

It’s our mission to give all who seek Illume's services a place to get the answers they need as well as achieve their family-building goals. Our whole team firmly believes that having knowledge about the fertility treatment process is empowering, and knowing how things work can be incredibly helpful along the way. 

When the answer to your fertility challenge is in vitro fertilization (IVF) treatment, that comes with its own set of unknowns, like "How long does the IVF process take?" and "Can I exercise or have sex during IVF?"

But the most common question we hear is usually "How many embryos will we have at the end of this process?" To answer that question, we have to talk about IVF attrition rates.

What is IVF attrition rate?

Everyone wants the best outcome possible, but it is always important to have realistic expectations about the IVF process. One aspect of in vitro fertilization (IVF) that is essential to understand is the attrition rate.

So, what is IVF attrition rate? This is the rate at which your viable genetic material (eggs or embryos) taper off once they are in the embryology lab and growing. 

In other words, the number of eggs that are retrieved are not likely to result in an equal amount of embryos. Instead, they will gradually decrease in number as they go from retrieved egg, to maturity, to fertilization, and then through the embryo growth stages.

The bottom line? Not every egg retrieved will become a viable embryo. As hard as this can be to accept, try to remember that attrition is completely normal (and expected).

It might be scary to hear the stats when we first go over them, but remember - this is exactly how conception works in the natural process as well. With IVF, we just have the privilege of seeing this natural attrition happen in real time in the embryology laboratory.

IVF by the Numbers: Attrition Rate Example

Let’s break IVF attrition down by using some concrete numbers so you can see how this might all play out in an average fertility treatment cycle. 

It all starts with the egg! As you may know by this point in your research, the first stage of IVF involves stimulating the ovaries to create as many dominant follicles as possible.

Here’s a quick recap: In a typical menstrual cycle, several follicles are created. One becomes dominant and the rest are reabsorbed back into the body. That dominant follicle releases an egg into the fallopian tube during ovulation and is fertilized by sperm at that point.

With IVF, we manipulate that normal cycle by getting as many of your follicles to grow to that dominant phase as possible (instead of just the one). It takes a special mix of medications to make this happen, and when the growth phase is complete (but before ovulation), we remove each egg from its follicle through a process called an egg retrieval.

Next, let's walk through the three phases of attrition together to better understand why not all eggs retrieved will create viable embryos.

A visual representation of the IVF attrition process.

Phase 1: Egg Retrieval 

Let’s say 12 eggs are retrieved on your egg retrieval day…

Unfortunately, not all 12 eggs will be viable (or useable). Why? Because only mature eggs will fertilize. While our goal is to retrieve all mature eggs, they naturally grow at different paces, leaving us with some variation in viability. We carefully assess each egg upon retrieval to determine maturity and viability.

During the follicular stimulation phase, we try to maximize the number of viable eggs by "triggering" ovulation at the optimal time, when the highest number of eggs will be mature. The "trigger shot" is your final injection in an IVF cycle before retrieval.

So, out of these 12 retrieved eggs, retrieved at the peak of average growth before ovulation, we expect that an average of approximately 80% will be mature.

That leaves us with 10 viable eggs.

Visual learner? Watch this video to see Nurse Monica explain this process further.

Phase 2: Fertilization

The fertilization process has to happen naturally overnight with partner or donor sperm in a laboratory. This happens one of two ways: conventional insemination or intracytoplasmic sperm injection (ICSI). Both are very effective and used for different reasons.

• Conventional insemination is when the egg is surrounded by a deposit of sperm in a petri dish. Because one sperm will find its own way into the egg for fertilization, this mimics natural selection as best we can in a laboratory setting. There are multiple reasons to choose this method, one of which is good sperm quality.
• Intracytoplasmic sperm injection (ICSI) is when an embryologist selects a single sperm and manually injects it into the egg to fertilize it. ICSI is used for a number of different reasons, one being male factor infertility.

Either way, we expect that 80% of the mature eggs will fertilize. Now we have 8 fertilized eggs (referred to from here on out as embryos). 

Phase 3: Embryo Growth & Development

The next big step is growing the embryos in the laboratory for the next 5-6 days. This is another phase where attrition should be expected. After 3 days, embryos have 6-8 cells. In general, most (if not all) embryos that fertilize will reach this stage.

The greatest attrition occurs between day 3 and day 5 or 6 (the blastocyst stage). A blastocyst is the final stage of embryo growth before we cryopreserve (freeze) them or perform an embryo transfer.

Only 30-50% of embryos growing on day 3 will reach the blastocyst stage.

So from our 8 embryos that initially fertilized, around 3-4 will be viable for transfer.

Note: If you're interested in getting your embryos tested prior to transfer, a biopsy will be performed at this stage and the sample(s) will be sent off for preimplantation genetic testing (PGT), prior to cryopreserving them.

Thinking about IVF?

Download our free guide to IVF to learn more about how much it costs, how long it typically takes, and how this fertility treatment can help you.

Why don't all eggs create healthy embryos?

This is a great question, with a somewhat unsatisfying answer: attrition is simply a natural selection process.

The good news, however, is that each phase of the attrition process reduces the likelihood of a non-viable embryo being transferred (that might result in the embryo not implanting successfully or lead to miscarriage, for example).

That being said, it can be hard to accept this process! You have every right to be frustrated or grieve the potential of your eggs and/or embryos that don't make it to the finish line. We know how hard you've worked to get to this point, and hearing those numbers decrease day-by-day can be incredibly disheartening.

Want extra support? Reach out to your nurse or navigator to schedule an appointment with a fertility counselor who understands the unique challenges of treatment.

A few things to note:

1. Every situation is different, so your percentages will likely look different than the ones above. Some patients will end up with more eggs or embryos than others. These are simply an average to help you set your expectations and understand the process.
2. The percentage of an egg or embryo's survival at each stage is based on the preceding number, not the original number.
3. Egg quality matters more than egg quantity. Try not to be disappointed if you don't get as many eggs on retrieval day as your friend or relative who also did IVF.
4. It's tough to predict how this process will go for each individual patient. As with everything else on a fertility journey, there's a lot of "wait and see," which can be nerve-wracking. Rest assured that your Care Team will update you on your numbers at each stage so you know what's going on.

What will my personal IVF attrition rate be?

These numbers may sound dramatic, but remember, in women under the age of 37, the transfer of just one single blastocyst gives a 50-55% chance of a healthy pregnancy! 

In women over the age of 37, that percentage can be lower, but with embryo testing and the transfer of a normal embryo, these women will have pregnancy rates of 50-55% as well.

Remember: not every situation is identical and many factors can affect your outcome, but this does provide a general outline as to what to expect. Whether you’re a heterosexual couple, LGBTQ+ dads-to-be, or LGBTQ+ moms-to-be, these numbers will still be your average rate of attrition.

So, no matter your situation, you can expect a similar scenario.

The Bottom Line: Attrition is Normal

The most important thing to remember is that attrition is normal and expected. And even just one embryo at the end of the cycle offers you an excellent chance at family building, which is the goal you had when you walked through your fertility clinic’s doors.

It’s also important to get the process started as soon as you’re ready. The sooner we can work together, the better chance you have of getting more embryos of a higher quality.

IVF is the most effective fertility treatment out there, and our whole team here at Illume Fertility is ready to help make your dreams come true, so reach out to us when you're ready.