Carnegie stage table

Embryology - 1 Dec 2023 Expand to Translate
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Carnegie Institute of Washington

Introduction

Carnegie stages are named after the famous US Institute which began collecting and classifying embryos in the early 1900's. Stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages covering the first 8 weeks post-ovulation.

See also the historic early work of Mall (1910)^[1] on embryonic and fetal growth.This staging system can also be applied to other species, see Carnegie Stage Comparison.

Week:	1	2	3	4	5	6	7	8
Carnegie stage:	1 2 3 4	5 6	7 8 9	10 11 12 13	14 15	16 17	18 19	20 21 22 23

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Links: Embryo Virtual Slides | Human Embryo Collections

Carnegie Stage Table

Weeks shown in the table below are embryonic post ovulation age, for clinical Gestational Age (GA) measured from last menstrual period, add 2 weeks.

Stage	Days (approx)	Size (mm)	Images (not to scale)	Events
1	1 (week 1)	0.1 - 0.15		fertilized oocyte, zygote, pronuclei
2	2 - 3	0.1 - 0.2		morula cell division with reduction in cytoplasmic volume, blastocyst formation of inner and outer cell mass
3	4 - 5	0.1 - 0.2		loss of zona pellucida, free blastocyst
4	5 - 6	0.1 - 0.2		attaching blastocyst
5	7 - 12 (week 2)	0.1 - 0.2		implantation
6	13 - 15	0.2		extraembryonic mesoderm, primitive streak, gastrulation
7	15 - 17 (week 3)	0.4		gastrulation, notochordal process
8	17 - 19	1.0 - 1.5		primitive pit, notochordal canal
9	19 - 21	1.5 - 2.5		Somitogenesis Somite Number 1 - 3 neural folds, cardiac primordium, head fold
10	22 - 23 (week 4)	2 - 3.5		Somite Number 4 - 12 neural fold fuses
11	23 - 26	2.5 - 4.5		Somite Number 13 - 20 rostral neuropore closes
12	26 - 30	3 - 5		Somite Number 21 - 29 caudal neuropore closes
13	28 - 32 (week 5)	4 - 6		Somite Number 30 leg buds, lens placode, pharyngeal arches
Stage 13/14 shown in serial embryo sections series of Embryology Program
14	31 - 35	5 - 7		lens pit, optic cup
15	35 - 38	7 - 9		lens vesicle, nasal pit, hand plate
16	37 - 42 (week 6)	8 - 11		nasal pits moved ventrally, auricular hillocks, foot plate
17	42 - 44	11 - 14		finger rays
18	44 - 48 (week 7)	13 - 17		ossification commences
19	48 - 51	16 - 18		straightening of trunk
20	51 - 53 (week 8)	18 - 22		upper limbs longer and bent at elbow
21	53 - 54	22 - 24		hands and feet turned inward
Stage 22 shown in serial embryo sections series of Embryology Program
22	54 - 56	23 - 28		eyelids, external ears
23	56 - 60	27 - 31		rounded head, body and limbs
Following this stage Fetal Development occurs until birth (approx 37 weeks)

The embryos shown in the table are from the Kyoto and Carnegie collection and other sources.

References

Historic Stages

Historic Disclaimer - information about historic embryology pages
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)