blas·​to·​cyst ˈbla-stə-ˌsist How to pronounce blastocyst (audio)
: the modified blastula of a placental mammal having an outer layer composed of the trophoblast

Examples of blastocyst in a Sentence

Recent Examples on the Web His team showed that mouse stem cells can self-organize into structures that resemble a blastocyst, which forms five or six days after sperm fertilizes an egg. Jennifer Ouellette, Ars Technica, 7 Apr. 2023 About five to six days after fertilization, an early-stage embryo, called a blastocyst, forms. Brian Barrett, WIRED, 27 Feb. 2024 Of those seven, only 25% to 50% will grow in the laboratory long enough to be considered a more mature embryo called a blastocyst, Feinberg said. Madeline Holcombe, CNN, 21 Feb. 2024 Finally—about five to six days after fertilization—the blastocyst implants itself into the uterus. ​wendy Wisner, Parents, 18 Nov. 2023 Su and her colleagues were able to characterize the RNA into five distinct genetic profiles or time periods of embryonic development: the oocyte or egg, zygote or fertilized egg, cleavage, morula and blastocyst stages. Deborah Balthazar, STAT, 17 Jan. 2024 Under a microscope, the structures looked similar to blastocysts—the early stage of an embryo—at days 8 and 9 of development. Jennifer Ouellette, Ars Technica, 7 Apr. 2023 But to keep growing, a blastocyst had to embed itself into the lining of a mother’s uterus. Amos Zeeberg (discover Web Editor), Discover Magazine, 15 July 2010 During this stage, more cell division takes place, and your blastocyst takes a ball-like shape. ​wendy Wisner, Parents, 18 Nov. 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'blastocyst.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


blasto- + -cyst

First Known Use

1876, in the meaning defined above

Time Traveler
The first known use of blastocyst was in 1876

Dictionary Entries Near blastocyst

Cite this Entry

“Blastocyst.” Dictionary, Merriam-Webster, Accessed 26 May. 2024.

Medical Definition


blas·​to·​cyst ˈblas-tə-ˌsist How to pronounce blastocyst (audio)
: the modified blastula of a placental mammal

More from Merriam-Webster on blastocyst

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