Carnegie Staging Guide

Carnegie Stage
Age (post ovulatory days)
Weeks post conception
Somite stage
Crown rump lenth (mm)
Morphological land marks
9
19-21
3
1-3
1.5-3.0
Head fold present
10
22
4
4-12
2.0-3.5
Neural tube closing. First and second branchial arches visible
11
24
4
13-21
2.5-4.5
Rostral neuropore closing. Otic placodes present. Optic vesicles formed.
26
4
21-29
3-5
Upper limb buds appear. Rostral neuropore closed. Caudal neuropore closing. Otic pits present. Three pairs of branchial arches visible.
28
4
30+
4-6
Embryo has C-shaped curve. Caudal neuropore closed. Upper limb buds flipper like. Four pairs of branchial arches visible. Lower limb buds appear. Otic vesicles present. Lens placodes distinct. Attenuated tail present.
32
5
 
5-7
Upper limbs paddle-shaped. Lens pits and nasal pits visible. Optic cups present.
33
5
 
7-9
Hand plates formed. Lens vesicles present. Nasal pits prominent. Lower limbs paddle-shaped. Cervical sinuses visible.
37
6
 
8-11
Foot plates formed. Pigment visible in retina. Auricular hillocks developing.
41
6
 
11-14
Digital rays clearly visible in hand plates. Auricle hillocks outline future auricle of external ear. Trunk beginning to straighten. Cerebral vesicles prominent.
44
7
 
13-17
Digital rays clearly visible in foot plates. Elbow region visible. Eyelids forming. Notches between the digital rays in the hand.
47.5
7
 
17-20
Limbs extend ventrally. Trunk elongating and straightening. Midgut herniation prominent. Prominent toe rays.
50.5
8
 
21-23.
Upper limbs longer and bent at elbows. Fingers distinct but webbed. Notches between the digital rays in the feet. Scalp vascular plexus appears.
52
8
 
22-24
Hands and feet approach each other. Fingers free and longer. Toes distinct but webbed. Stubby tail present.
54
8
 
25-27
Toes free and longer. Eyelids and auricles or external ears more developed
56
8
 
28-30
Head more rounded and shows human characteristics. External genitalia still have sexless appearance. Distinct bulge still present in umbilical cord caused by herniation of intestines.

* Adapted from the Carnegie Stage definitions (O'Rahilly R and Muller F [1987] Developmental Stages in Human Embryos. Carnegie Institute. Washington, Publication no. 637) by Bullen P and Wilson D (1997) The Carnegie Staging of Human Embryos: a Practical Guide. In "Molecular Genetics of Early Human Development" Ed. Strachan T, Lindsay S and Wilson DI. Bios Scientific Publishers.