Carnegie Stage |
Age (post ovulatory days) |
External Characteristics |
Secondary Characteristics |
Histology Backup |
Size (mm) |
10 |
22 |
Mainly open neural groove, up to 12 somites. | 1.5 - 3mm | ||
11 |
24 |
Anterior neuropore closing, posterior still open. | 2.5-4.5mm | ||
12 |
26 |
No limb buds or minimal upper limb bud. | Posterior neuropore may be open. | Epithelial proliferation marks formation of lung bud. Otocysts closing. | 3-5mm |
13 |
28 |
4 limb buds - tiny lower limb buds. | R/L lung buds visible. Optic Vesicle closed and endolymph appendage. | 4-6mm | |
14 |
32 |
Tapering upper limb - still no hand plate. | Open lens pit. | Indented lens disc. Adenohypophyseal AH pouch prominent. | 5-7mm |
15 |
33 |
Hand plate now visible. | Lens pit closed. | Lens pit closure and retinal pigment. Lobar buds on main bronchi now. | 7-9mm |
16 |
37 |
Foot plate visible and retinal pigment. | Pharangeal arch 3 receeding. Auricular hillocks. | Intestinal mesentary established. Frankly branched bronchi. | 8-11mm |
17 |
41 |
Digital rays of hand and full round foot plate. | Full auricular hillocks now present. | Early palate, duodenal follicular appearance. Lens cavity crescentric as disk thickens. | 11-14mm |
18 |
44 |
Notched hand plate and +/- elbow. | Eye-lid folds in late specimens. | Oesophagus has distinct submucous and muscular layers, semi circular canals. | 13-17mm |
19 |
47.5 |
Prominent toe rays. | Limbs all extend nearly directly forwards. | Renal vesicles just cavitating. | 17-20mm |
20 |
50.5 |
Stubby fingers, toe notches, vascular plexus in head. | Elbows bent. Hands still well apart. | Renal vesicles with S shaped cavities and capsules. | 21-23mm |
21 |
52 |
Fingers longer, getting closer. Toes not just notches, may touch. | "Tactile Pads" on end of fingers. | Sub epithelial layer becomes cellular stalk. AH partly absorbed. | 22-24mm |
22 |
54 |
Fingers touch, may overlap. Vascular plexus 3/4 of the way up head. | Ear features far more prominent. | Some mature glomeruli. AH stalk remnants at ends only. | 25-27mm (middle group) |
23 |
56 |
Vascular plexus almost to vertex. Limbs generally. | Eye-lids may be starting to fuse at margins. | Numerous glomeruli (Fetus-bone marrow forming). | 28-30mm (middle group: full range is 23-32mm) |
* 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.