The Carnegie stages are a standardized system of 23 stages used to chronologically describe vertebrate embryonic development. The stages are delineated by structural developments rather than size or days. This summary covers the key points about the Carnegie stages, including that they provide a unified developmental timeline for embryos, are based on structural changes rather than time or size, and were established based on work in the 1940s and 1980s to standardize descriptions of embryonic development.

1. CARNEGIE STAGE

4. 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. IN
THE HUMAN BEING ONLY THE FIRST 60 DAYS OF DEVELOPMENT ARE COVERED; 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 INSTITUTION OF
WASHINGTON.

5. CARNEGIE EMBRYOS STAGE
Week: 1 2 3 4 5 6 7 8
Carnegi
e stage:
1 2 3 4 5 6 7 8 9
10 11 1
213
14 15 16 17 18 19
20 21 2
223

7. FERTILIZED OOCYTE, ZYGOTE, PRONUCLEI
• THE EARLY HUMAN ZYGOTE WHERE THE MALE AND FEMALE
PRONUCLEI (CENTRE OF IMAGE) HAVE NOT YET COMBINED TO FORM
THE SINGLE ZYGOTE NUCLEUS. THESE PRONUCLEI ARE THE NUCLEI
FROM THE SPERMATOZOA (SPERM) AND OOCYTE (EGG) AND
CONTAIN ALL THE NUCLEAR GENETIC MATERIAL (CHROMOSOMES,
DNA, GENES).
• TWO OF THE EGG'S POLAR BODIES (RIGHT, 3 O'CLOCK POSITION OF
IMAGE) ARE SHOWN AT THE EDGE OF THE EGG CYTOPLASM. THESE
POLAR BODIES CONTAIN THE EXCESS DNA FROM THE MEIOTIC
DIVISIONS OF THE EGG.
• THE ZONA PELLUCIDA (EDGE OF IMAGE) FORMS A SPECIALISED
THICK EXTRACELLULAR MATRIX LAYER AROUND BOTH THE EGG AND
THE DEVELOPING CONCEPTUS FOR THE FIRST WEEK.
• MITOCHONDRIA IN THE CYTOPLASM CONTAIN ADDITIONAL GENES
AND IN HUMANS THESE MITOCHONDRIAL GENES ARE ENTIRELY
DERIVED FROM THE OOCYTE.

8. WEEK 1, 2 - 3 DAYS, SIZE 0.1 - 0.2 MM
MORULA, ZONA PELLUCIDA, BLASTOMERES
First cell mitotic divisions of the
zygote forming initially 2
blastomeres that continue to
divide to form the morula, a
"berry", a solid mass of cells.This
early mitosis is a unique
embryonic cell cycle (M, S, M
phases) compared to adult (M,
G1, S, G2, M phase). With virtually
no G1 or G2phases this results in
a reduction in cytoplasmic

9. LOSS OF ZONA PELLUCIDA, FREE BLASTOCYST
THAT TROPHOBLAST,EMBRYOBLAST

10. WEEK 1-2, SIZE 0.1 - 0.2 MM
ADPLANTATION AND IMPLANTATION COMMENCES,
INCREASE IN HCG
Stage 4 sees the attached blastocyst
begin implantation into the maternal
uterine lining epithelium and underlying
stroma. The entire cellular products of
the original fertilisation event are now
referred to as the conceptus, this will
include embryonic and extra-embryonic
tissues of the fetal membranes and
placenta.

11. IMPLANTATION SIZE 0.1 - 0.2 MM

12. STAGE 6
The bilaminar (two layer) embryo is
now about 0.2 mm diameter in size.
The three extra embryonic spaces
(amniotic, primitive yolk sac and
chorionic) are present.The large
chorionic cavity is surrounded by the
cell layers extending to form
chorionic villi. These villi are the
beginning of the functional units of
the placenta.

13. GASTRULATION, NOTOCHORDAL PROCESS
SIZE 0.4 MM

14. HUMAN EMBRYONIC STAGE 8 OCCURS DURING
WEEK 3 BETWEEN 17 TO 19 DAYS.
THE EMBRYO IS NOW 1.0 - 1.5 MM IN SIZE
Gastrulation is continuing as cells migrate from the
epiblast, continuing to form mesoderm.
Mesoderm lies between the ectoderm and endoderm as a
continuous sheet except at the buccopharyngeal and
cloacal membranes. These membranes have ectoderm
and endoderm only and will lie at the rostral (head) and
caudal (tail) of the gastrointestinal tract.
From the primitive node a tube extends under the
ectoderm in the opposite direction to the primitive streak.
This tube forms first the axial process then notochordal
process, then finally the notochord.
The notochord is a key to embryonic folding and
regulation of ectoderm and mesoderm differentiation. It
lies in the rostrocordal axis and the embryonic disc will
fold either side ventrally, pinching off a portion of the yolk
sac to form the lining of the gastrointestinal tract.

15. HUMAN EMBRYONIC STAGE 9 OCCURS
DURING WEEK 3 BETWEEN 19 TO 21 DAYS
The embryo is now 1.5
to 2.5 mm in size and
somites have begun to
form and number
between 1 to 3 somite
pairs during this stage

16. SOMITE NUMBER 4 - 12 NEURAL FOLD
FUSES
SIZE 2 - 3.5 MM

17. SOMITE NUMBER 13 - 20 ROSTRAL
NEUROPORE CLOSES SIZE 2.5 - 4.5MM

18. SOMITE NUMBER 21 - 29 CAUDAL
NEUROPORE CLOSES SIZE 3– 5MM

19. ZOMITE NUMBER 30 LEG BUDS, LENS
PLACODE, PHARYNGEAL ARCHES SIZE 4 –
6MM

20. LENS PIT, OPTIC CUP, NOSE HOLE SIZE 5 –
7MM

21. LENS VESICLE, NASAL PIT, HAND PLATE SIZE
7 – 9MM

22. NASAL PITS MOVED VENTRALLY, AURICULAR
HILLOCKS, FOOT PLATE SIZE 8 – 11 MM

23. FINGER RAYS SIZE 11 – 14 MM

24. OSSIFICATION COMMENCES SIZE 13 – 17MM

25. STRAIGHTENING OF TRUNK SIZE 16 – 18 MM

26. UPPER LIMBS LONGER AND BENT AT ELBOW SIZE
18 – 22 MM

27. HANDS AND FEET TURNED INWARD SIZE 22 –
24 MM

28. EYELIDS, EXTERNAL EARS SIZE 23 – 28MM

29. ROUNDED HEAD, BODY AND LIMBS SIZE 27 –
31MM

30. ЭХ СУРВАЛЖ
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• HTTPS://EN.WIKIPEDIA.ORG/WIKI/CARNEGIE_STAGES