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Carnegie stages

In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo.

The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos. It only covers the first 60 days of development; at that point the term embryo is usually replaced with the term fetus.

It was based on work by Streeter (1942) and O'Rahilly and Müller (1987). The name "Carnegie stages" comes from the Carnegie Institute.

While the Carnegie stages provide a universal system for staging and comparing the embryonic development of most vertebrates, other systems are occasionally used for the common model organisms in developmental biology, such as the Hamburger-Hamilton stages in the chick.



Days are approximate, and reflect the days since the last ovulation before pregnancy ("Postovulatory age").

Stage 1: 1 days

Stage 2: 3 days

Stage 3: 4 days

  • blastocyst and blastocoele
  • embryonic disk
  • trophoblast and embryoblast

Stage 4: 5-6 days

  • syncytiotrophoblast
  • cytotrophoblast
  • amniotic ectoderm

Stage 5 (a-c): 7-12 days

Stage 6: 13-15 days

  • primitive streak
  • primitive groove
  • chorionic villi
  • secondary yolk sac

Stage 7: 15-17 days

Stage 8: 17-19 days

  • primitive pit

Stage 9: 19-21 days

Stage 10: 21-23 days

Stage 11: 23-26 days

Stage 12: 26-30 days

  • upper limb buds

Stage 13: 28-32 days

  • septum primum
  • foramen primum

Stage 14: 31-35 days

Stage 15: 35-38 days

Stage 16: 36-42 days

Stage 17: 42-44 days

Stage 18: 44-48 days

  • septum secundum

Stage 19: 48-51 days

Stage 20: 51-53 days

Stage 21: 53-54 days

Stage 22: 54-58 days

Stage 23: 56-60 days

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Carnegie_stages". A list of authors is available in Wikipedia.
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