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.
Stages
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
Stage 4: 5-6 days
- syncytiotrophoblast
- cytotrophoblast
- amniotic ectoderm
Stage 5 (a-c): 7-12 days
Stage 6: 13-15 days
Stage 7: 15-17 days
- gastrulation
- neural plate
- start of hematopoiesis
- notochord
Stage 8: 17-19 days
Stage 9: 19-21 days
Stage 10: 21-23 days
Stage 11: 23-26 days
Stage 12: 26-30 days
- upper limb buds
