Eight eggs retrieved. Why is only one embryo left?

During ovarian stimulation, the ultrasound showed a dozen or so follicles, and you thought this cycle would go well. On retrieval day, the nurse said they got eight eggs. The next day, a phone call: five fertilized. On day five, another call: one made it to blastocyst.

Between eight and one there were four or five days and three phone calls, and none of them told the whole story. So you start looking up other people’s numbers online, and the more you read, the more anxious you get. Someone got four embryos from eight eggs. Someone else got three from six. You wonder whether you did something wrong, whether it was the nights you didn’t sleep well, or whether this clinic just isn’t good.

First, one thing to say clearly: this drop is real, and it happens in steps. Where those steps are, and why numbers fall at each one, is something you can ask about and get answers to. Only once you have those answers can you tell whether to switch, and what to switch.

1. Five stages between a follicle and a transferable embryo

The full chain looks like this:

Follicles counted on ultrasound → eggs actually retrieved → mature eggs among them → eggs successfully fertilized → blastocysts formed after 5–6 days of culture → (if chromosome screening is done) embryos suitable for transfer.

Some are lost at every stage. That is how the technology works, not a mistake by any one clinic.

So “eight eggs retrieved, only one left” is incomplete information. It squeezes five stages into a single number. What you actually need to know is this: of the eight, how many were mature? Of the mature eggs, how many fertilized? Of those, how many were still developing on day 3, and how many on day 5? All of these numbers are in your medical records. No one has simply walked you through them in one go.

2. The first three stages: counted, retrieved and mature are three different numbers

Stage one: a follicle is not an egg. What the ultrasound shows is a follicle, a small sac of fluid. The doctor aspirates that fluid, and the egg is inside it. Some follicles contain no egg to begin with, and some eggs can’t be drawn out cleanly. So “12 follicles counted, 8 eggs retrieved” is very common, and on its own it doesn’t mean anyone did anything wrong.

Stage two: an egg is not a mature egg. Only eggs that have reached a specific stage of development (usually recorded as MII in your chart) can be fertilized. Follicles in the same cycle don’t all grow at the same pace, and the timing of retrieval is a compromise across the whole group, so a few eggs will always be a little early or a little late. How many are lost here depends relatively strongly on the stimulation protocol and the timing of the trigger shot (the injection that prompts final maturation). This is one of the few points in the chain where the protocol can be adjusted, so it is worth asking about on its own.

Stage three: fertilization. In conventional IVF, prepared sperm and eggs are placed together and fertilization happens on its own. In ICSI, a single sperm is injected directly into the egg, usually when sperm quality is not ideal or fertilization rates were low in a previous cycle. A common misunderstanding is worth clearing up here: ICSI can solve the problem of sperm not getting into the egg. It cannot solve problems with the egg itself. It is not an upgrade that makes things better for everyone. Whether to use it depends on the male partner’s test results and how previous cycles went.

3. The last two stages: blastocyst culture and chromosome screening

Stage four is where the largest losses happen. After fertilization, embryos are cultured continuously until they form blastocysts on day 5–6, and a substantial share stop developing between day 3 and day 5. Most of the embryos lost at this stage are ones that could not have continued developing anyway.

This is hard to hear, but it is exactly the point of this stage: it is better for development to stop in the lab than inside your body. Many people see “only one blastocyst” as a loss. In fact, that one has been selected through the process. It is not what happens to be left over from five.

Stage five only exists if PGT-A (preimplantation genetic testing for aneuploidy) is done. A few cells are taken from the blastocyst to check whether the number of chromosomes is normal. The share of euploid embryos (those with a normal chromosome count) falls as the woman’s age rises. This is a widely accepted trend in reproductive medicine, and large studies have confirmed it repeatedly (for example, the 2014 study by Franasiak and colleagues in Fertility and Sterility, which analyzed more than 15,000 blastocyst biopsy results).

This also explains why two people with the same eight eggs retrieved can end up with very different final numbers depending on age, and why the difference mostly arises in these last two stages rather than at retrieval. Whether to do PGT-A, and in what situations, is not handled identically in guidelines from different countries. Your treating doctor decides, based on your age, previous cycles and any history of miscarriage.

4. When to suspect it isn’t just luck

In the following situations, it is worth taking your complete cycle records for a proper review (in other words, a second opinion):

• The share of mature eggs is low again and again: this suggests there may be room to adjust the trigger timing or the stimulation protocol.
• Fertilization rates are repeatedly very low, especially with conventional IVF: male factors need to be reassessed, along with whether to switch to ICSI.
• Most embryos stop developing around day 3 after fertilization: at this point, the lab’s culture conditions are something you should ask about.
• Several cycles in a row show consistently poor numbers: once can be luck, but when it keeps happening, it is a pattern.

But the other half needs to be said too:

Changing clinics, or changing countries, can change the protocol, the lab conditions and the quality of communication. It cannot change your age, and it cannot change the condition of the eggs themselves. So if any clinic promises you that you will “definitely get more eggs,” “definitely get blastocysts” or that success is “guaranteed,” you can rule it out on the spot. That isn’t caution. It’s common sense.

The same applies to treatments we arrange ourselves. For diminished ovarian reserve, there is a category of treatments injected into the ovary (autologous platelet-rich plasma (PRP), mesenchymal stem cells and others), and they are not cheap. In a July 2026 price list we have, an intraovarian injection of adipose-derived mesenchymal stem cells is JPY 3,520,000 per session (tax included). It is offered at some clinics as self-pay treatment not covered by insurance. The published evidence is still at a fairly early stage: most studies so far are small, no large randomized controlled trial has shown that it improves live birth rates, and the findings are not consistent. The procedure itself also carries risks, such as bleeding and infection from fat harvesting and ovarian puncture.

We offer this service, and we will tell you everything in the paragraph above, word for word. It is better to decide after you understand the limits of the evidence than to decide on hope.

5. Next step: gather these three records before deciding whether to switch

Don’t make a decision based on a single “1.” Before your next appointment, collect these three records:

• Retrieval record: how many eggs were retrieved in total, and how many were mature (MII).
• Fertilization report: the method used (conventional IVF or ICSI), and how many fertilized normally.
• Embryo culture record: cell count and grade for each embryo on day 3; how many became blastocysts on day 5–6 and the grade of each; and, if PGT-A was done, the screening results.

With those three documents in hand, ask your doctor four questions:

• At which stage did most of the drop happen in this cycle?
• Is that stage related to the stimulation protocol, and can it be adjusted?
• Given my age and test results, what is a reasonable expectation if I do another cycle?
• If I do, how long should I wait before starting?

If you already have these records but can’t make sense of the abbreviations and grades, you can send them to us (with your name, ID numbers and other identifying details removed). We will start by marking the numbers at each stage so you can ask the right questions at your next consultation. We don’t diagnose, and we won’t reach conclusions on the doctor’s behalf. What we can do is make sure you are no longer left worrying over a single number on its own.