IVF Attrition Rate: Why Don’t All Eggs Create Embryos?
So now you are ready to take the next big step in your family building journey: IVF. It is very exciting, but at the same time, it can also be stressful.
As a physician at RMA of Connecticut, my number one goal is to help the men and women that walk through our doors family-build. They often come in with questions, concerns, and an understandable amount of anxiety. This is a big step for anyone, and I respect them for taking the leap. It’s my mission to give all who seek our services a landing place with answers and results.
And when the answer to their problem is IVF, that comes with its own set of new understandings and concerns. One of the biggest: How many embryos will we have at the end of this?
The Realities of IVF Attrition Rate
Everyone wants the best outcome possible, including me, but it is always important to have realistic expectations about the IVF process.
One aspect of the IVF process that is very important to understand is the attrition rate.
IVF attrition rate is the rate at which viable options (eggs, embryos) taper off once they are in the 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 through the embryo growth stages. Not every egg a woman produces will become a viable embryo.
Our biggest takeaway: This is totally normal!
It might be scary when we first go over the numbers together, but this is exactly how conception works in the natural process as well. With IVF, we have the privilege of seeing this natural attrition happen in real time in a laboratory.
IVF by the Numbers: An Attrition Rate Example
Let’s break it down with numbers so you can see how this might all play out in an average situation…
Need a refresher on the IVF Process?
As you may know by this point in your research, the first phase of IVF is to stimulate the ovaries and create as many dominant follicles as possible.
Here’s a quick recap: In a normal menstrual cycle, women create several follicles. 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 into 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.
Let’s Say 12 Eggs Were Retrieved…
Unfortunately, not all 12 eggs will be viable, or useable. Why? Because only mature eggs will fertilize. While our goal is to have all mature eggs, they naturally grow at different paces and thus will leave us with some variation in viability. During the follicular stimulation phase, we try to maximize the number of viable eggs by “triggering” at the optimal time, when most eggs will be mature. The “Trigger Shot” is final injection before retrieval.
So out of these 12 retrieved eggs, taken at the peak of average growth without ovulating, we expect that an average of approximately 80% will be mature. That leaves us with 10 viable eggs.
Now, We Fertilize the 10 Eggs…
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 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 being good sperm quality.
ICSI, or intra-cytoplasmic sperm injection, is when an embryologist selects a single sperm and manually injects it into the egg, fertilizing it that way. This 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 embryos.
Those 8 Embryos Will Grow Through Multiple Embryo Stages…
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 rate comes from day 3 to day 5-6, or the blastocyst stage. A blastocyst is the final stage of the embryo before we cryopreserve them or transfer to a patient. Only 30-50% of embryos growing on day 3 will reach the blastocyst stage.
So from our 8 embryos that initially fertilized, about 3-4 will be viable for transfer.
Let’s Recap the IVF Attrition Rate
Before you zip through these numbers, there are a couple things to note…
- Every situation is different, so your percentages may look different than these. Some will have better success; others will have lower numbers. These are simply an average and should help you set your expectations.
- The percentage of survival at each stage is based on the preceding number. Not the original.
Phase 1: Egg retrieval
80% move forward
Example rate: 12 eggs retrieved → 10 mature
Phase 2: Egg Fertilization
80% move forward
Example Rate: 10 mature eggs → 8 fertilized
Phase 3: Embryo Growth
30-50% become blastocysts.
Example Rate: 8 fertilized eggs → 3-4 Blastocysts
What Will My Personal Attrition Rate in IVF Look Like?
These numbers sound dramatic, but remember, in a woman under the age of 37, transfer of a single blastocyst gives a 50-55% chance for pregnancy!
In women over the age of 37, the number 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.
Certainly not every situation is identical and other factors can affect the outcome, but this does provide a general outline as to what to expect. Whether you’re a heterosexual couple, Dads to be, or Moms to be, these numbers will still be your average rate of attrition.
No matter your situation, you should expect a similar attrition rate.
The most important thing to remember is that this is a normal process. 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 when you’re ready. The sooner we get to work together, the better chance we have at getting you a higher embryo count with better quality. IVF is the most effective fertility treatment out there, and we’re ready to make your dreams come true!
Ready to start your own fertility journey?