8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 1/15
Week -2
(Clinical Week 1)
Day Menstrual cycle Event
1 Menstrual Phase
Menstrual Cycle changes: Uterine endometrium (loss), Ovary (Follicle Development)
2
3
4
5Proliferative
Phase
Menstrual Cycle changes: Uterine endometrium (proliferation), Ovary
(Follicle Development)
6
7
Week -1
(Clinical Week 2)
Day Menstrual cycle Event
8Proliferative
Phase
9
Menstrual Cycle - Mid
proliferative
10
11
12
13
Menstrual Cycle - Late Proliferative
14
Ovulation
Capacitation
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 2/15
Week 1
Week 1 (Clinical Week 3)
Week 1 summary
Day Stage Event
1
SecretoryPhase
Stage 1
Fertilization, Secretory Phase
2 Stage 2
Morula, Blastula
3
Blastocyst Development
4 Stage 3
Blastocyst Hatching (zona pellucida lost)
5
Late Secretory, Blastocyst (freefloating)
6 Stage 4 Adplantation
7 Stage 5
Week 2
Week 2 (Clinical Week 4)
Day Stage Event
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 3/15
8
Implantation
9
10
11
12
13 Stage 6
Chorionic Cavity
14
Week 3
Week 3 (Clinical Week 5)
Day Stage Event
15
16 Stage 7
17
18 Stage 8
Neural neurogenesis, neural groove and folds are first seen
19
20 Stage 9
Musculoskeletal somitogenesis, first somites form and continue to be added in
sequence caudally
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 4/15
Neural the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still
completely open
Neural Crest mesencephalic neural crest is visible[1]
21 Heart cardiogenesis, week 3 begins as paired heart tubes.
Week 4
Week 4 (Clinical Week 6)
Day Stage Event
22Stage
10
Neural Crest differentiation at spinal cord level from day 22 until day 26
Neural neural folds begin to fuse near the junction between brain and spinal cord, when Neural Crest cells are arising mainly
from the neural ectoderm
Neural Crest trigeminal, facial, and postotic ganglia components visible [1]
Neural Crest migration of vagal level neural crest cells begins (7-10 somite stage)
Neural rostral neural tube forms 3 primary brain vesicles (week 4)
Respiratory Week 4 - laryngotracheal groove forms on floor foregut.
23 Heart begins to beat in Humans by day 22-23, first functioning embryonic organ formed.
24Stage
11
Thyroid thyroid median endodermal thickening in the floor of pharynx
Neural rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and
terminal lips and may occur in two areas simultaneously. The two lips, however, behave differently.
Ventricular System Optic ventricle appears and the neural groove/tube space is initially filled with amniotic fluid.[2]
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 5/15
25Stage
12
Pituitary Week 4 hypophysial pouch, Rathke's pouch, diverticulum from roof
Liver septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae [3]
Neural caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2)
Neural secondary neurulation begins
Ventricular System onset of the ventricular system and separates the ependymal from the amniotic fluid.[2]
Neural Crest cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus
arteriosus [1]
Neural Crest vagal neural crest enter the foregut (20-25 somite stage)
26
27
28Stage
13
Neural the neural tube is normally completely closed, ventricular system now
separated from amniotic fluid. Neural crest at spinal level is segregating, and spinal ganglia are in series with the somites. Spinal
cord ventral roots beginning to develop.[4]
telencephalon cavity appears
Liver epithelial cord proliferation enmeshing stromal capillaries[3]
Smell Crest comes from the nasal plates[5]
Skin 4 weeks - simple ectoderm epithelium over mesenchyme
Skin 1-3 months ectoderm- germinative (basal) cell repeated division of generates stratified epithelium; mesoderm-
differentiates into connective tissue and blood vessels
Vision Optic vesicle lies close to the surface ectoderm. The surface ectoderm overlying the optic vesicle, in response to this
contact, has thickened to form the lens placode.[6]
Week 5
Week 5 (Clinical Week 7)
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 6/15
Day Stage Event
29
Pituitary Week 5 elongation, contacts infundibulum, diverticulum of diencephalon
Heart Week 5 septation starts, atrial and ventricular
Respiratory Week 5 left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
Respiratory Week 5 to 17 lung histology - pseudoglandular
Hearing Week 5 cochlear part of otic vesicle elongates (humans 2.5 turns)
30
31
32Stage
14
Placodes sensory placodes, lens pit, otocyst, nasal placode, primary/secondary
vesicles, fourth ventricle of brain
Mesoderm continued segmentation of paraxial mesoderm (somite pairs), heart prominence
Head 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum
Body - heart, liver , umbilical cord, mesonephric ridge visible externally as bulges.
Limb upper and lower limb buds growing
Neural first appearance of the future cerebral hemispheres. Cerebellar plate differentiated to an intermediate layer, and future
rhombic lip identifiable[7]
Ventricular System Subarachnoid space initially as irregular spaces on the ventral surface of the spinal cord. 16228957
Liver hepatic gland and its vascular channels enlarge, hematopoietic function appears[3]
Eye - Lens the lens placode is indented by the lens pit.[6]
33Stage
15 Neural cranial nerves (except olfactory and optic) are identifiable in more advanced embryos[8]
Eye - Lens the lens pit is closed. The lens vesicle and optic cup lie close to the surface ectoderm and appear to press against the
surface.[6]
34
35 Vision 35 to 37 days retinal pigment present
Week 6
Week 6 (Clinical Week 8)
Day Stage Event
36 Pituitary Week 6 - connecting stalk between pouch and oral cavity degenerates
Parathyroid Week 6 - diverticulum elongate, hollow then solid, dorsal cell proliferation
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 7/15
Thymus Week 6 - diverticulum elongate, hollow then solid, ventral cell proliferation
Adrenal Week 6 - fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla neural crest cells from adjacent
sympathetic ganglia
Respire Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes
Tongue Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes gustatory papilla, caudal midline near
the foramen caecum (week 6 to 7 - nerve fibers approach the lingual epithelium)
37Stage
16
Neural first parasympathetic ganglia, submandibular and ciliary, are identifiable[9]
Limb upper limb bud nerves median nerve, radial nerve and ulnar nerve entered into hand plate, myoblasts spindle shaped and
oriented parallel to limb bud axis.
Heart outflow tract elliptical configuration with four cushions, the two larger fusing at this stage. Semilunar valve leaflets form
at the downstream end of the cushions
Head lip and palate components of the upper lip, medial nasal prominence and maxillary process present, median palatine
process appears.
Eyelid prior to the development of the eyelids, one small sulcus or groove forms above the eye (eyelid groove) and another
below it.[6]
38
39
40
41Stage
17
Neural telencephalon areas of the future archicortex, paleocortex, and neocortex, visible. Beginning of future choroid plexus[10]
Smell olfactory nerve fibres enter the brain[5]
Neural primordium of the epidural space appears first on the ventral part of the vertebral canal and develops rostro-caudally[11]
Eyelid sulcus (groove) above and below eye deepen and eyelid folds develop (below first and then above)[6]
42 Heart separation of common cardiac outflow (aortic arch and pulmonary aorta)
Week 7
Week 7 (Clinical Week 9)
Day Stage Event
43
Pancreas Week 7 to 20 pancreatic hormones secretion increases, small amount maternal insulin
Respiratory Week 7 - enlargement of liver stops descent of heart and lungs
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 8/15
44 Stage 18
Limb Bone forms by endochondrial ossification and throughout embryo replacement of cartilage with bone (week 5-12).
Neural Smell vomeronasal fibres and nervus terminalis[5]
Liver obturation due to epithelial proliferation, bile ducts became reorganized, continuity between liver cells and gut[3]
Ventricular System duramater appears and spaces surround the circumference of the spinal cord, which coalesce and contain
many blood vessels.[11]
Uterus Vagina opening of the Müllerian duct to the coelomic cavity formed as an invagination of the coelomic epithelium[12]
45 Liver (stage 18 to 23) biliary ductules developed in periportal connective tissue
produces ductal plates that receive biliary capillaries[3]
46
47
48 Stage 19 Neural accessory olivary nucleus appears[13]
Uterus Müllerian duct grows independently from the invagination of the coelomic epithelium during stages 19-23[12]
Eyelid the upper and the lower eyelids meet at the outer canthus[6]
49
Week 8
Week 8 (Clinical Week 10)
Day Stage Event
50 Stage
20
Head scalp vascular plexus visible
Limb upper limbs begin to rotate ventrally
Neural amygdaloid body has at least four individual nuclei[13]
oculomotor nerve shows a dorsolateral and a ventromedial portion
rhombic lip (rhombencephalon) formation of the cerebellum (intermediate layer) and of the cochlear nuclei
cerebellum cell layer (future Purkinje cells) develops
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 9/15
choroid plexuses of the fourth and lateral ventricles
Eyelid the inner canthus is established.[6]
51 Gastrointestinal Tract anal membrane perforates
52Stage
21 Neural cortical plate appears in the area of future insula [14]
Limb upper and lower limbs rotate
Intraembryonic Coelom pericardioperitoneal canals close
53
54Stage
22
Neural neocortical fibres project to epithalamus, to dorsal thalamus, and to mesencephalon[14]
Limb fingers and toes lengthen
Smell Stage 22 to early fetal period - migratory streams of neurons from the subventricular zone of the olfactory bulb towards
the future claustrum[5]
Uterus Vagina fused duct (uterovaginal canal) bifurcated at the caudal portion at Carnegie stages 22 and 23[12]
55
Genital 8 Weeks Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione
Genital 8 to 12 Weeks - hCG stimulates testosterone production
Tongue Week 8 - nerves penetrate epitheilai basal lamina and synapse with undifferentiated, elongated, epithelial cells (taste
bud progenitor cell)
56 Stage
23
Stage 23 defines the end of the embryonic (organogenesis) period
Mesoderm heart prominence, ossification continues
Head nose, eye, external acoustic meatus, eyelids, external ears, rounded head
Body - straightening of trunk, umbilical cord, intestines herniated at umbilicus
Limb upper limbs longer and bent at elbow, hands and feet turned inward, foot with separated digits, wrist, hand with separated
digits
Extraembryonic Coelom chorionic cavity is now lost by fusion with the expanding amniotic cavity
Neural rhombencephalon, pyramidal decussation present, nuclei and tracts similar to those present in the newborn cerebellum
present as only a plate connected to midbrain and hindbrain through fibre bundles [15]
Axial Skeleton vertebral column 33 or 34 cartilaginous vertebrae (20-33 mm in total length), vertebral pedicles, articular and
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 10/15
transverse processes identifiable (no spinous processes) [16]
Week 8
Stomach Week 8 - Gastrin containing cells in stomach antrum. Somatostatin cells in both the antrum and the fundus.
Uterus Development 56 days - paramesonephric duct fusion (female)
Week 9
(Clinical Week 11)
Day Stage Event
57 Fetal Period
Hearing Week 9 - mesenchyme surrounding membranous labrynth (otic capsule) chondrifies
Smell Embryonic/Fetal transition - localized incomplete lamination of the olfactory bulb[5]
58
59
60
61
62
63
Week 9 - CRL 43 mm, femur length 6 mm
9 weeks CRL 50 mm - Genital genitalia in both sexes look identical[17]
uterus - paramesonephric ducts come into apposition with the urorectal septum and begin to fuse
Week 10
(Clinical Week 12)
Day Stage Event
64
Gastrointestinal Tract Week 10 intestines in abdomen
Pituitary growth hormone and ACTH detectable
Pancreas Week 10 glucagon (alpha) differentiate first, somatostatin (delta), insulin (beta) cells differentiate, insulin secretion
begins
Tongue Week 10 shallow grooves above the taste bud primordium
Stomach Week 10 - Glucagon containing cells in stomach fundus.
Nail Development fingernails appear
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 11/15
Hearing - Outer Ear Development Week 10 - Meatal plug extends in a disc-like fashion, the meatus is boot-shaped with a narrow
neck and the sole of the meatal plug spreading widely to form the future tympanic membrane medially. Proximal portion of the
neck starts to be resorbed.
65
66
67
68
69
70 Week 10 - CRL 55 mm, femur length 9 mm, biparietal diameter 17 mm
Week 11
(Clinical Week 13)
Day Stage Event
71
Thyroid colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis
Stomach Week 11 - Serotonin containing cells in both the antrum and the fundus.
72
73
74
75
76
77 Week 11 - CRL 68 mm, femur length 12 mm, biparietal diameter 20 mm
Second Trimester
(Clinical Week 14) Second Trimester
Week Stage Event
12
Clinical
second
trimester
Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm
Hearing Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic
space) around membranous labrynth and fills with perilymph
Genital male and female external genital differences observable
Respiratory Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
Tongue Week 12 - first differentiated epithelial cells (Type II and III)
Genital female genital canal (80 days) formed with absorption of the median septum
13 Tongue Week 12 to 13 - maximum synapses between cells and afferent nerve fibers
Hearing - Outer Ear Development Week 13 - Meatal plug disc-like, innermost surface in contact with the primordial
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 12/15
malleus, contributes to the formation of the tympanic membrane.
14
Tongue Week 14 to 15 - taste pores develop, mucous
Ovary Development 100 days - primary follicles present
Nail Development toenails appear
Head Development facial skeleton remodelling begins
15
Pancreas glucagon detectable in fetal plasma.
Spleen Week 15 -alpha-smooth muscle actin (alpha-SMA)-positive reticulum cells scattered around the arterioles. [18]
Fetal Timeline
16 14 cm
Hearing Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form
petrous portion of temporal bone. Continues to ossify to form mastoid process of temporal bone.
Pituitary adenohypophysis fully differentiated
Respiratory Week 16 to 25 lung histology - canalicular
Hearing - Outer Ear Development Week 16.5 - External auditory meatus is fully patent throughout its length, lumen is
still narrow and curved.
Skin 4 months - basal cell- proliferation generates folds in basement membrane; neural crest cells- (melanocytes) migrate
into epithelium; embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the
dense ct layer is another loose ct layer that will form the subcutaneous layer. Ectoderm contributes to nails, hair follictles
and glands. Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells
of nail field. Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous
and sweat glands.
primary follicles begin to form in the ovary and are characterized by an oocyte
glandular urethra forms and skin folds present
17
Neural - Brain development histology week 17
18
Tongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 13/15
Skin vernix caseosa covers skin
Spleen Week 18 - alpha-SMA-positive reticulum cells increase in number and began to form a reticular framework. An
accumulation of T and B lymphocytes occurred within the framework, and a primitive white pulp was observed around
the arterioles. [18]
Hearing - Outer Ear Development week 18 - External auditory meatus is already fully expanded to its complete form.
19
20
Pituitary week 20 to 24 growth hormone levels peak, then decline
Skin lanugo, skin hair
Skin 5 months - Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands; Other cords
elongate and coil to form sweat glands; Cords in mammary region branch as they elongate to form mammary glands.
21
22
Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus,
parietooccipital fissure, and hippocampic fissures presen t[19]
Spleen - Week 22 - antigenic diversity of the reticular framework was observed, and T and B lymphocytes were
segregated in the framework. T lymphocytes were sorted into the alpha-smooth muscle actin-positive reticular
framework, and the periarteriolar lymphoid sheath (PALS) was formed around the arteriole. B lymphocytes aggregated in
eccentric portions to the PALS and formed the lymph follicle (LF). The reticular framework of the LF was alpha-SMA-
negative. [18]
23
24
Respiratory Week 24 to 40 lung histology - terminal sac
Spleen Week 24 - marginal zone appeared in the alpha-smooth muscle actin-positive reticular framework around the
white pulp.[18]
Earliest potential survival expected if born
ovarian follicles can consist of growing oocytes surrounded by several layers of granulosa cells
25 Respiratory end month 6 alveolar cells type 2 appear and begin to secrete surfactant
Third Trimester
(Clinical Week 28) Third Trimester
Week Stage Event
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 14/15
Clinical third
trimester
Hearing 3rd Trimester - vibration acoustically of maternal abdominal wall induces startle
respone in fetus.
27
28 Respire Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs
29
30Genital male gonad (testes) descending
31
32 Nail Development fingernails reach digit tip
33 Neural brain cortical sulcation - primary sulci present[19]
34 Neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present[19]
35
36
Nail Development toenails reach digit tip
Lens Development - lens growth and interocular distance plateaus after 36 weeks of gestation [20]
37
38 Birth
Clinical Week 40
Heart pressure difference closes foramen ovale leaving a fossa ovalis
Thyroid TSH levels increase, thyroxine (T3) and T4 levels increase to 24 h, then 5-7 days postnatal decline to
normal levels
Adrenal - zona glomerulosa, zona fasiculata present
Postnatal
Week Stage Event
+1
+2
+3
+4 Vision Development - eye globe growth plateaus after 42 weeks of gestation [20]
+5
Month
Testis | Spermatozoa - about 2 months of age, primordial germ cells (gonocytes) are replaced by adult dark (Ad) and pale
(Ap) spermatogonia forming the spermatogonial stem cell (SSC) population that at puberty will commence differentiation
into spermatozoa.
Year
Year 1 Neural Hearing (6 months to 5 years) thalamocortical afferents to the deeper cortical layers mature and are the first source of
input to the auditory cortex[21]
Year 2
Year 3 Adrenal - Year 3 zona reticularis present
8/6/2019 Weeks Timetable
http://slidepdf.com/reader/full/weeks-timetable 15/15
4
5 Neural Hearing - (5 to 12 years) commissural and association axons in the superficial cortical layers allows communication
between subdivisions of the auditory cortex [21]
37
38
