It's one of the most exciting and nerve-racking moments of the journey: after the retrieval, the fertilization and the waiting, a short report lands in your inbox — how many embryos were created, how they were graded, and what the genetic testing found. And then the panicked googling begins: what is euploid? Why does it say mosaic next to one? And is a 5BB good or bad?
Let's go through an email like this together, line by line.
What a typical email looks like
Subject: Embryo Report — PGT-A Results
Dear parents,
We are happy to share the final report for your cycle. Of the eggs retrieved, 6 embryos reached the blastocyst stage and were biopsied for PGT-A. The results:
Embryo #1 — 4AA — Euploid
Embryo #2 — 5AB — Euploid
Embryo #3 — 3BB — Euploid
Embryo #4 — 4BC — Low-level mosaic
Embryo #5 — 5AA — Aneuploid
Embryo #6 — 3CB — Aneuploid
All euploid embryos have been cryopreserved. Please schedule a call to discuss next steps.
Six lines — and inside them, three different layers of information. Let's take them apart.
Layer 1: the number and the letters (4AA, 5AB...)
This is the embryologist's visual grade — how developed the embryo is and how its cell groups look. I've written a separate, detailed post about grading, so here's just the essence: the grade is a visual assessment, it varies between clinics and even between embryologists, and it is not a genetic test.
Layer 2: the genetic result of the PGT-A test
Euploid (chromosomally normal) — the PGT-A test found the correct number of chromosomes. These are the embryos your clinic will want to transfer first, and they're the reason transfer success rates in surrogacy are as high as they are.
Aneuploid (chromosomally abnormal) — an extra or missing chromosome was found. In the vast majority of cases these embryos won't be transferred, because the chance of a healthy pregnancy is very low. And yes — look at embryo #5 in the example: an excellent visual grade (5AA) with an abnormal genetic result. It happens, and it's exactly why the test is done.
Mosaic — the confusing middle: the biopsy found both normal and abnormal cells. And here it's worth pausing.
Let's talk about mosaic embryos
A few things worth knowing before the word scares you:
- The biopsy takes a handful of cells from the embryo's outer layer (the one that becomes the placenta) — not from the part that becomes the fetus itself. The picture it gives is partial by nature.
- There's a difference between a low-level mosaic (a small share of abnormal cells) and a high-level / complex mosaic (a large share, or several chromosomes involved). The first is closer to normal; the second is more concerning.
- Mosaic embryos have been transferred many times around the world and have led to healthy babies. In some cases the embryo "self-corrects" during development.
- Whether to transfer a mosaic embryo, when, and in what order of priority — that's a decision to make together with your fertility doctor and a genetic counselor, based on the specific chromosome involved and the level of mosaicism. Not based on Facebook groups, and not based on this post either.
In our example: three frozen euploids are a good starting point, and the mosaic (#4) is a "backup card" kept in storage — it isn't discarded, and most clinics will hold it for a future conversation if it's ever needed.
The clinic knows the sex too — but won't write it without asking
PGT-A counts chromosomes — including the sex chromosomes — so the clinic knows, for every embryo, whether it's male or female. At most clinics this won't appear in the report automatically: they'll ask your permission first, because some parents simply prefer not to know. It's worth deciding in advance what you want — this information can affect your choices later, when you pick which embryo to transfer.
One last thing
This email is a milestone, not a final grade. I've seen families with two embryos become overjoyed parents, and families with eight who needed several transfers. The numbers matter — but they are not yet the story.
