Can Embryo Grade Tell You the Gender?
Last reviewed 2026-10-27
No. An embryo grade such as 4AA, 5AB or 3BB describes how the embryo looks under a microscope and carries no information about chromosomes — so it carries none about sex. Only a genetic test identifies sex. If your clinic has given you grades but not a PGT-A report, nobody at that clinic knows the sex of your embryos either.
What the grade actually means
Blastocyst grading, usually on the Gardner system, is three observations written as a number and two letters.
| Part of the grade | What it describes | Scale |
|---|---|---|
| The number (1–6) | Expansion — how far the blastocyst has grown and whether it has started to hatch out of its shell | 1 is early, 5–6 is hatching or hatched |
| First letter (A–C) | Inner cell mass — the compact group of cells that becomes the fetus | A is many tightly packed cells; C is few and loose |
| Second letter (A–C) | Trophectoderm — the outer layer that becomes the placenta, and the layer that is biopsied for testing | A is many cells forming a cohesive layer; C is few and uneven |
So 4AA is a well-expanded blastocyst with a good inner cell mass and a good outer layer. It is a photograph taken by an embryologist, and a good photograph correlates with a better chance of implantation. It is not a karyotype, and a high-grade embryo can still be chromosomally abnormal.
Where the “top embryos are male” idea comes from
This belief is widespread in patient forums and it has a real origin: a body of work has reported that male embryos tend to develop slightly faster in culture, so that among embryos reaching blastocyst earliest, males may be modestly over-represented. From there it is a short and wrong step to “my 5AA must be a boy.”
Why it is wrong as a basis for any decision: whatever the size of the effect, it is a small statistical skew across populations of embryos, not a property of your embryo. It cannot tell you about a single case, which is exactly where you want to use it. The grade of one embryo is compatible with either sex, and planning around it is planning around noise.
A practical consequence worth knowing: in Canada you may be given grades and deliberately not be told the sex, even when PGT-A was performed. That is not the clinic being unhelpful — section 5(1)(e) of the Assisted Human Reproduction Act prohibits identifying the sex of an in vitro embryo outside the sex-linked-disorder exception. See where it is legal.
What does tell you the sex
A trophectoderm biopsy sent for PGT-A. About five cells from the outer layer, sequenced, with the sex chromosomes read as part of the chromosome count. That is the only route, and the process is set out on how it works. If you are in a country where sex selection is lawful and the test has been done, ask for the laboratory's own report rather than a verbal summary — it lists every embryo, including the mosaic and no-result ones that summaries tend to drop.
Can you tell the gender of an embryo from its grade?
No. Grades such as 4AA or 5AB describe expansion, inner cell mass and outer cell layer under a microscope. They contain no chromosomal information, so they cannot indicate sex.
Is a 4AA embryo more likely to be a boy?
No basis for planning. Male embryos have been reported to develop slightly faster on average, which is a small population-level skew, not a property of an individual embryo. Any given high-grade embryo is about as likely to be either sex.
What does 5AB mean?
A blastocyst at expansion stage 5 — hatching — with grade A inner cell mass and grade B trophectoderm. It describes appearance and developmental stage, nothing about chromosomes.
Why won't my clinic tell me the sex of my embryos?
In some countries they are not permitted to. Canada's Assisted Human Reproduction Act prohibits identifying the sex of an in vitro embryo except to prevent, diagnose or treat a sex-linked disorder. Elsewhere it may be clinic policy.
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