Day 5 blastocyst
A blastocyst-stage embryo cultured for five days after fertilisation, the most common stage at which embryos are transferred or frozen.
In plain English
It's an embryo grown to day 5, the stage most clinics prefer for transfer or freezing.
Why it matters
Reaching day 5 in the lab helps identify embryos that are developing well, though not every embryo survives to this stage.
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.