Embryo
A fertilised egg that has begun dividing and developing, from the day after fertilisation until roughly the end of the eighth week of pregnancy.
In plain English
It's what an egg becomes once it's fertilised and starts dividing into more cells.
Why it matters
Everything from grading to freezing to transfer decisions in IVF is about assessing and handling embryos.
Related terms
Guides that cover this
Written by patients, not clinicians. This page has not yet been reviewed by a named fertility professional, so it explains published guidance and points you to the original source instead of giving medical advice. It is not medical advice. Decisions about your treatment belong with your own clinic. Read our editorial policy and corrections policy.