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blastocyst
Pronunciation: BLAS-toe-sist
An early-stage embryo, typically 5-6 days after fertilization, consisting of about 100 cells arranged in a hollow sphere.
Full Definition
A blastocyst is a highly developed pre-implantation embryo that forms 5-6 days after fertilization. It consists of an outer layer called the trophectoderm (which becomes the placenta) and an inner cell mass (which becomes the fetus). The blastocyst stage represents a critical milestone in embryo development, as only viable embryos typically reach this stage. In IVF, blastocyst transfer is often preferred over earlier-stage transfers because it allows for better embryo selection and may improve implantation rates.
Usage
Usage note: Not capitalized unless beginning a sentence.
In Context
- "The embryologist selected a high-grade blastocyst for transfer." — Procedure note
- "Blastocyst culture extends embryo development to improve selection criteria." — Research paper
Also known as
day 5 embryo
day 6 embryo
Contrasted with
cleavage-stage embryo
Don't confuse with
blastula
morula