Fetal Development

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Introduction

Relative fetal sizes
<html5media height="400" width="360">File:fetal growth.mp4</html5media> This page shows some key events of human development during the fetal period (weeks 9 to 37) following fertilization. The long Fetal period (4x the embryonic period) is a time of extensive growth in size and mass as well as ongoing differentiation of organ systems established in the embryonic period. Clinically this period is generally described as the Second Trimester and Third Trimester. Many of the critical measurements of growth are now carried out by ultrasound and this period ends at birth.


Many different systems formed in the embryonic period (organogenesis) grow and differentiate further during the fetal period and do so at different times. For example, the brain continues to grow and develop extensively during this period (and postnatally), the respiratory system differentiates (and completes only just before birth), the urogenital system further differentiates between male/female, endocrine and gastrointestinal tract begins to function. Also consider the systems (respiratory, cardiac, neural) that will still not have their final organization and function determined until after birth.

Changing fetal proportions, not size growth.

Click Here to play on mobile device | movie page

Use the links below to get more detailed information about this period of development.


Historic Embryology
Embryology History George Streeter In 1949 the embryologist George Streeter[1] used the replacement of cartilage within the humerus by bone marrow as an arbitrary definition of the embryo to fetus transition.
"If the onset can be recognized in a given specimen, that specimen is straightway classed as a fetus."


Fetal Links: fetal | Week 10 | Week 12 | second trimester | third trimester | fetal neural | Fetal Blood Sampling | fetal growth restriction | birth | birth weight | preterm birth | Developmental Origins of Health and Disease | macrosomia | BGD Practical | Medicine Lecture | Science Lecture | Lecture Movie | Category:Human Fetus | Category:Fetal
Historic Embryology  
1940 Fetus Physiology
Carnegie Fetal: 95 | 96 | 142 | 145 | 184 | 211 | 217 | 300 | 362 | 448 | 449 | 538 | 590 | 607 | 625 | 662 | 693 | 847 | 858 | 922 | 928 | 948 | 972 | 1318 | 1388 | 1455 | 1591 | 1597b | 1656 | 1686 | 2250a | 2250b | 3990 | 5652 | 6581 | 7218


Fetal Graphs: Crown-Rump Length (CRL) | Third trimester CRL | Head Circumference | Head Circumference 2nd Trimester | Liver Weight | Pancreas Weight | Thymus Weight | Small Intestine Length | Large Intestine Length | Length and Weight Changes | Fetal Development

Some Recent Findings

Fetus (week 10)
  • Functional connectome of the fetal brain [2] "Large-scale functional connectome formation and re-organization is apparent in the second trimester of pregnancy, making it a crucial and vulnerable time window in connectome development. Here we identified which architectural principles of functional connectome organization are initiated prior to birth, and contrast those with topological characteristics observed in the mature adult brain. A sample of 105 pregnant women participated in human fetal resting-state fMRI studies (fetal gestational age between 20 and 40 weeks). Connectome analysis was used to analyze weighted network characteristics of fetal macroscale brain wiring. We identified efficient network attributes, common functional modules and high overlap between the fetal and adult brain network. Our results indicate that key features of the functional connectome are present in the second and third trimesters of pregnancy. Understanding the organizational principles of fetal connectome organization may bring opportunities to develop markers for early detection of alterations of brain function. The fetal to neonatal period is well known as a critical stage in brain development. In this study, we evaluate the network topography of normative functional network development during connectome genesis in utero Understanding the developmental trajectory of brain connectivity provides a basis for understanding how the prenatal period shapes future brain function and disease dysfunction." neural
  • Fetal brain growth portrayed by a spatiotemporal diffusion tensor MRI atlas computed from in utero images[3] "Altered structural fetal brain development has been linked to neuro-developmental disorders. These structural alterations can be potentially detected in utero using diffusion tensor imaging (DTI). However, acquisition and reconstruction of in utero fetal brain DTI remains challenging. Until now, motion-robust DTI methods have been employed for reconstruction of in utero fetal DTIs. However, due to the unconstrained fetal motion and permissible in utero acquisition times, these methods yielded limited success and have typically resulted in noisy DTIs. Consequently, atlases and methods that could enable groupwise studies, multi-modality imaging, and computer-aided diagnosis from in utero DTIs have not yet been developed. This paper presents the first DTI atlas of the fetal brain computed from in utero diffusion-weighted images. For this purpose an algorithm for computing an unbiased spatiotemporal DTI atlas, which integrates kernel-regression in age with a diffeomorphic tensor-to-tensor registration of motion-corrected and reconstructed individual fetal brain DTIs, was developed. Our new algorithm was applied to a set of 67 fetal DTI scans acquired from healthy fetuses each scanned at a gestational age between 21 and 39 weeks. The neurodevelopmental trends in the fetal brain, characterized by the atlas, were qualitatively and quantitatively compared with the observations reported in prior ex vivo and in utero studies, and with results from imaging gestational-age equivalent preterm infants. Our major findings revealed early presence of limbic fiber bundles, followed by the appearance and maturation of projection pathways (characterized by an age related increase in FA) during late 2nd and early 3rd trimesters. During the 3rd trimester association fiber bundles become evident. In parallel with the appearance and maturation of fiber bundles, from 21 to 39 gestational weeks gradual disappearance of the radial coherence of the telencephalic wall was qualitatively identified. These results and analyses show that our DTI atlas of the fetal brain is useful for reliable detection of major neuronal fiber bundle pathways and for characterization of the fetal brain reorganization that occurs in utero. The atlas can also serve as a useful resource for detection of normal and abnormal fetal brain development in utero."
  • Stresses and strains on the human fetal skeleton during development[4] "Mechanical forces generated by fetal kicks and movements result in stimulation of the fetal skeleton in the form of stress and strain. This stimulation is known to be critical for prenatal musculoskeletal development; indeed, abnormal or absent movements have been implicated in multiple congenital disorders. However, the mechanical stress and strain experienced by the developing human skeleton in utero have never before been characterized. Here, we quantify the biomechanics of fetal movements during the second half of gestation by modelling fetal movements captured using novel cine-magnetic resonance imaging technology. ...We find that fetal kick force increases significantly from 20 to 30 weeks' gestation, before decreasing towards term. However, stress and strain in the fetal skeleton rises significantly over the latter half of gestation. This increasing trend with gestational age is important because changes in fetal movement patterns in late pregnancy have been linked to poor fetal outcomes and musculoskeletal malformations."
  • The role of three-dimensional ultrasonography fetal lung volume measurement in the prediction of neonatal respiratory function outcome[5] "Respiratory distress is commonly encountered among premature babies immediately after birth resulting in significant neonatal morbidity or mortality. To evaluate the possible correlation between three dimensional fetal lung volumes (FLVs) and neonatal respiratory outcomes. A cohort study included 100 pregnant women who participated in the study and were divided into two groups; group A (n: 50 - women pregnant ±34-37 weeks) and group B (n: 50 - women pregnant ±37+1 to 40 weeks). A three dimensional measurement of the right fetal lung was made using virtual organ computer-aided analysis (VOCAL) software then correlated to neonatal respiratory functions namely Apgar score at birth and the occurrence of respiratory distress syndrome (RDS). In group A, FLV was negatively correlated with Apgar score and the occurrence of RDS. In group B, FLV showed no statistical correlation with Apgar score and the occurrence of RDS. Three dimensional fetal lung volumes might be an accurate noninvasive predictor for the development of RDS among preterm fetuses."
More recent papers  
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More? References | Discussion Page | Journal Searches | 2019 References | 2020 References

Search term: Fetal Development | Foetal Development | Second Trimester | Third Trimester

Older papers  
These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.

See also the Discussion Page for other references listed by year and References on this current page.

  • Size and location of the kidneys during the fetal period[6] "The level of the left kidney was higher than the level of the right kidney in the fetal period. The posterior surface relations to the ribs showed certain ascendance during gestation, corresponding to vertebral levels. However, fetal kidneys do not reach the same level as adults at full term. The kidneys move farther apart from the midline of the body during the fetal period. The dimensions, weight, and volume of the kidneys increased with gestational age during the fetal period. The ratio between kidney weights and fetal body weights were determined, and we observed that the ratio decreased during the fetal period. There were no sex or laterality differences in any parameter." (See also Renal System Development)
  • Development and Function of the Human Fetal Adrenal Cortex: A Key Component in the Feto-Placental Unit[7] "The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone and its sulfate, precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis." (See also Endocrine - Adrenal Development)

Reading

  • Human Embryology (3rd ed.) Larson Chapter 15: Fetal development and the Fetus as Patient p481-499
  • The Developing Human: Clinically Oriented Embryology (8th ed.) Moore and Persaud Chapter 6: The Fetal Period: Ninth Week to Birth
  • Color Atlas of Clinical Embryology (2nd ed.) Moore, Persaud and Shiota Chapter 3: 9th to 38th weeks of human development p50-68
Fetal growth icon.jpg
 ‎‎Fetal Development
Page | Play
Fetal length and weight change

Fetal length change

Fetal Development - Length - Weight
Gestational age Fertilization age Length Mass
(LMP) (GA weeks) (weeks) (cm) (g)
8 (embryonic) 6 1.6 (crown to rump) 1
9 7 2.3 2
10 8 3.1 4
11 (fetal) 9 4.1 7
12 10 5.4 14
13 (second trimester) 11 7.4 23
14 12 8.7 43
15 13 10.1 70
16 14 11.6 100
17 15 13 140
18 16 14.2 190
19 17 15.3 240
20 18 16.4
25.6 (crown to heel)
300
21 19 26.7 360
22 20 27.8 430
23 21 28.9 501
24 22 30 600
25 23 34.6 660
26 24 35.6 760
27 25 36.6 875
28 (third trimester) 26 37.6 1005
29 27 38.6 1153
30 28 39.9 1319
31 29 41.1 1502
32 30 42.4 1702
33 31 43.7 1918
34 32 45 2146
35 33 46.2 2383
36 34 47.4 2622
37 35 48.6 2859
38 36 49.8 3083
39 37 50.7 3288
40 38 51.2 3462
41 39 51.7 3597
42 40 51.5 3685
References [8][9][10]

Ultrasound CRL Data

The collapsed table below shows measurement data from a recent ultrasound study.[11]

Fertilization and Gestational Age - Crown-Rump Length (ultrasound
Fertilization Age
(days)
Gestational Age
GA (week.day)
Crown-Rump
Length (mm)
37 5.2 1
38 5.3 2
39 5.4 3
40 55 3
41 5.6 4
42    Week 4 6 4
43 6.1 5
44 6.2 6
45 6.3 7
46 6.4 8
47 6.5 9
48 6.6 10
49    Week 5 7 11
50 7.1 11
51 7.2 12
52 7.3 12
53 7.4 13
54 7.5 14
55 7.6 15
56    Week 6 8 17
57 8.1 18
58 8.2 19
59 8.3 20
60 8.4 21
61 8.5 22
62 8.6 22
63    Week 7 9 23
64 9.1 24
65 9.2 26
66 9.3 27
67 9.4 28
68 9.5 29
69 9.6 31
70    Week 8 10 34
71 10.1 36
72 10.2 37
73 10.3 38
74 10.4 39
75 10.5 39
76 10.6 40
77    Week 9 11 44
78 11.1 45
79 11.2 47
80 11.3 48
81 11.4 52
82 11.5 55
83 11.6 56
84    Week 10 12 57
85 12.1 58
86 12.2 60
87 12.3 61
88 12.4 63
89 12.5 64
90 12.6 65
91    Week 11 13 68
92 13.1 70
93 13.2 72
94 13.3 74
95 113.4 76
96 135 77
97 13.6 80
98    Week 12 14 81
99 14.1 84
100 14.2 85
101 14.3 86
102 14.4 87
Reference: Table data measured by ultrasound, adapted from Westerway (2015) PDF and[11]
Links: ultrasound | Fetal Development

Second Trimester

Fetus - second trimester
(ultrasound)
  • Second Trimester
  • Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm.

Begin by working through the features present in the early 10 week female fetus. Then look in detail at the head development in a 12 week fetus.

Week 13 to Week 16

(GA Week 15-18)

  • Growth - rapid growth continues
  • Head - head has straightened up
    • eyes at the front part of the face but still widely separated
    • outer ear has moved (relatively) from upper part of neck to the side of the head
  • Musculoskeletal - ossification is proceeding
    • skeleton now visible on an x-ray
  • Integumentary - body is covered with lanugo

Week 17 to Week 20

(GA Week 19-21)

  • Growth - Length growth begins to slow.
    • body parts have acquired their relative proportions.
  • Integumentary - vernix caseosa
    • sebaceous glands begin to secrete and vernix caseosa comes to cover the skin to prevent damage by amniotic fluid.
  • Neural - Spinal cord myelinization begins
  • Adipose Tissue - brown fat is forming
  • Musculoskeletal - active movements of the fetus in the uterus (kicks)

Week 21 to Week 25

(GA Week 23-27)

  • Integumentary / Vision - eyelids and eyebrows developed
    • lanugo a darker color and vernix caseosa is thicker.
    • skin is sometimes very wrinkled (high growth, lack of subcutaneous fat)
    • fingernails are visible
  • Growth - face and body are usually as they will be at birth.
  • Fetuses born after the 25th week of gestation are generally viable
10 Week Fetus head images
Human- fetal week 10 head A.jpg Human- fetal week 10 head B.jpg Human- fetal week 10 head C.jpg Human- fetal week 10 head D.jpg

Then look in detail at the head development in a 12 week fetus showing both forms of ossification in the skull.

12 Week Fetus head images
Fetal head lateral.jpg Fetal head medial.jpg Fetal head section.jpg

Timeline

Second Trimester Timeline 
Links: human timeline | first trimester timeline | second trimester timeline | third trimester timeline
Week
Stage
Event
12
Clinical second trimester Fetal head lateral.jpg 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 Week 13 - Meatal plug disc-like, innermost surface in contact with the primordial malleus, contributes to the formation of the tympanic membrane.  

14
tongue Week 14 to 15 - taste pores develop, mucous

ovary 100 days - primary follicles present

nail toenails appear

Head Development facial skeleton remodelling begins

Hearing - Inner Ear Development Week 14 GA 16 - neural-crest-derived melanocytes, now intermediate cells of the stria vascularis, tightly integrate with Na+ /K+ -ATPase-positive marginal cells, which started to express KCNQ1 in their apical membrane.[12]

15
  Pancreas glucagon detectable in fetal plasma.

spleen Week 15 -alpha-smooth muscle actin (alpha-SMA)-positive reticulum cells scattered around the arterioles.[13]

16
14 cm Fetal size change.jpg 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.

Hearing - Inner Ear Development Week 16 GA 18 - cells in the outer sulcus express KCNJ10 and gap junction proteins GJB2/CX26 and GJB6/CX30, but these are not expressed in the spiral ligament.[12] gap junction cartoon

neural - Cerebrum development of the periinsular sulci (week 16-17, GA 18-19 weeks)[14]


integumentary 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
Brain week 17 histology.jpg Neural - Brain development histology week 17

Cerebellum Magnetic Resonance Imaging (MRI) can study the developing cerebellum from 17 to 18 weeks (GA 19 to 20 weeks).

tooth Week 17 - First papilla of the permanent dentition appear (first molar) immediately behind the second milk molar, milk teeth are well advanced (Fetus 180 mm).

18
Bailey095.jpgtongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia

integumentary 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.[13]

Hearing - Outer Ear Development week 18 - External auditory meatus is already fully expanded to its complete form.

neural - Cerebrum central sulci and opercularization of the insula (week 18-20, GA 20-22 weeks)[14]

19
  neural week 19 neuronal migration ends and the radial glial cells that aided the migration now become transformed into astrocytes and astrocytic precursors.[15]
20
  pituitary week 20 to 24 growth hormone levels peak, then decline

integumentary lanugo, skin hair

integumentary 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.

touch pacinian corpuscle begin to develop[16]

21
   
22
  Gray0038.jpg Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present[17]

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. [13]

neural - Cerebrum covering of the posterior insula (week 22-24, GA 24-26 weeks)[14]

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.[13]

tooth Week 24 - Permanent incisors and canines appear.

Earliest potential survival expected if born

ovary 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

neural - Cerebrum closure of the laeteral sulcus (Sylvian fissure or lateral fissure) (week 25-26, GA 27-28 weeks)[14]

26
  touch pacinian corpuscle well developed[16]
Systems  
Systems: bone timeline | eye neural crest timeline | heart abnormality timeline | hearing EAM timeline | muscle timeline | ovary timeline | placental villi timeline | shoulder timeline | smell timeline | spleen timeline | ventricular timeline

Third Trimester

Fetus - third trimester
(historic image)

Third trimester Crown-Rump Length graph.jpg

Third trimester Crown-Rump Length

Fetal weight change.jpg


  • Vibration acoustically of maternal abdominal wall induces startle respone in fetus.
  • Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs.
  • Week 37 to 38 Birth.

Week 26 to Week 29

(GA Week 28-31)

  • Integumentary / Vision - eyes are opened again and eyebrows and eyelashes are well formed
    • pupillary membrane disappears.
  • Integumentary - hair grows, subcutaneous adipose tissue deposits round the whole body, becomes chubby and plump

Week 30 to Week 34

(GA Week 32-36)

  • Integumentary - body becomes chubby and the skin is pink
    • fingernails have reached the ends of the fingers
    • toenails are visible
  • Genital - testicles descend


Timeline

Third Trimester Timeline
Links: human timeline | first trimester timeline | second trimester timeline | third trimester timeline
Week
Stage
Event
Clinical third trimester Fetal size change.jpg hearing 3rd Trimester - vibration acoustically of maternal abdominal wall induces startle respone in fetus.
27
 
28
  respiratory Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs
29
 

tooth Week 29 - Permanent premolars (correspond to the milk molars) appear.

30
   

Genital male gonad (testes) descending

31
 
32
  nail fingernails reach digit tip
33
  neural brain cortical sulcation - primary sulci present[17]
34
  neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present[17]
35
   
36
  Frazer006 bw600.jpg Nail Development toenails reach digit tip

Lens Development - lens growth and interocular distance plateaus after 36 weeks of gestation[18]

37
   
38
Birth Newborn.jpg 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

Systems  
Systems: bone timeline | eye neural crest timeline | heart abnormality timeline | hearing EAM timeline | muscle timeline | ovary timeline | placental villi timeline | shoulder timeline | smell timeline | spleen timeline | ventricular timeline


Links: Third Trimester

Growth

Fetal Head Growth

Second trimester Second and third trimesters
Fetal head growth circumference graph02.jpg Fetal head growth circumference graph01.jpg

Fetal Neural

Brain size embryonic (week 4, 5, 6, and 8) and late fetal (third trimester)

Relative brain size embryonic (week 4, 5, 6, and 8) and late fetal (third trimester)

  • During the fetal period there is ongoing growth in size, weight and surface area of the brain and spinal cord. Microscopically there is ongoing: cell migration, extension of processes, cell death and glial cell development.
  • Brain - folding of the initially smooth surface (Insular cortex, Gyral and Sulcal development)
  • Neural development will continue after birth with substantial growth, death and reorganization occuring during the postnatal period
Fetal Fissure Development Timeline Neural Development
Brain fissure development 03.jpg Neural-development.jpg
Links: Scaled Fissures 13-21 weeks | Fissures 13-21 weeks | Brain Sylvian Fissure | Scaled Brain and Ventricles 13-21 weeks | Scaled Brain, Ventricles and Ganglia 13-21 weeks | Limbic Tract 13-19 weeks | Brain and Ventricles 13-21 weeks | Sylvian Fissure Movie | Neural System Development | Magnetic Resonance Imaging Timeline human development


Links: Neural System Development

|}

Fetal Endocrine

Fetal thymus growth

Pituitary Hormones

  • HPA axis established by week 20
  • Pituitary functional throughout fetal development

Thyroid Hormone

  • required for metabolic activity, also in the newborn
  • important for neural development

Parathyroid Hormone

  • newborn has total calcium levels (approx 20 grams) accumulated mainly in the 3rd trimester (weeks 28–40)
  • fetal parathyroid hormone (PTH) potentially available from 10–12 weeks and PTH does not cross the placenta
  • fetus relatively hypercalcemic, active transplacental transport of Ca2+ to fetus
  • maternal serum - calcium ions (Ca2+), inorganic phosphate (Pi) and PTH concentrations are within the non-pregnant normal range throughout pregnancy.
  • maternal bone turnover increases in the 3rd trimester.

(Based on Endocrinology - Materno—fetal calcium balance)

Pancreatic Hormones

  • maternal diabetes can affect fetal pancreas development (increase in fetal islet beta cells).

Gonadal Hormones

  • testosterone - required during fetal development for external genital development and internal genital tract in male.
  • estrogens - secreted inactive precursor converted to active form by placenta.


Links: Endocrine System Development | Endocrinology - Control of steroid production in the fetal gonads | Neuroscience - The Effect of Sex Hormones on Neural Circuitry

Fetal Respiratory

  • week 4 - 5 embryonic
  • week 5 - 17 pseudoglandular
  • week 16 - 25 canalicular
  • week 24 - 40 terminal sac
  • late fetal - 8 years alveolar
Links: Respiratory System Development

Fetal Genital

  • ovary and testis development
  • external genital development
  • testis descent
Tests descent beginning Tests descent end
Testis-descent start.jpg Testis-descent end.jpg
Links: Genital System Development

Fetal Renal

Human fetal kidney
Human fetal kidney (GA week 12)
  • week 32-34 nephron development completed
  • term birth nephron number per kidney about 1 million (300,000 to 2 million)

Nephron development has four identifiable developmental stages:

  1. Vesicle (V) stage (13-19 weeks, second trimester)
  2. S-shaped body (S) stage ( 20-24 weeks, second trimester)
  3. Capillary loop (C) stage (25-29 weeks, third trimester)
  4. Maturation (M) stage (infants aged 1-6 months, neonatal and postnatal)


Links: Fetal Renal | renal

Fetal Gastrointestinal

Fetal small Intestine length growth graph.jpg Fetal large Intestine length growth graph.jpg
Fetal small Intestine length growth
Fetal large Intestine length growth

Fetal developmental features include: the growth and rotation of intestines initially herniated outside the ventral body wall; changes in mesenteries; development of the blood supply and tract wall.

The initial functions of the tract with amionic fluid swallowing and the accumulation of both secretions and swallowed components within the large intestine as meconium.


Links: intestine | gastrointestinal

Fetal Integumentary

4 months
  • basal cell - proliferation generates folds in basement membrane.
  • neural crest cells - (melanocytes) migrate into epithelium. These are the pigment cell of the skin.
  • 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 follicles and glands.
    • Cords of these cells extend into mesoderm forming epithelial columns. These form hair follicles, sebaceous and sweat glands.
  • Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field.

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. These glands will complete development in females at puberty. Functional maturity only occurs in late pregnancy.
Fetal integumentary histology 01.jpg
Links: integumentary


Fetal Palate

Levator veli palatini skeletal muscle contacted by the lesser palatine nerve.[19] The lesser palatine nerve (posterior palatine nerve) is a branch of the maxillary nerve (CN V2), one of two palatine nerves that descends through the greater palatine canal, and emerges by the lesser palatine foramen


Links: palate

Fetal Surgical Procedures

There are a range of fatal abnormalities that are potentially amenable to surgical intervention, see recent review link Maternal-Fetal Surgical Procedures.[20]

Some examples include:


Maternal

There are many maternal physiological changes during and after pregnancy. This section introduces just the anatomical changes that must occur to simply accomodate the growing fetus.

<html5media width="480" height="360">https://www.youtube.com/embed/yE-l1stWkT4</html5media>

Make Room for Baby! (2017)

BrauneB1.jpg

The Position of the Uterus and Fetus at Term (1872).[21]

Links: Maternal Development | MP4 | Museum of Science and Industry, Chicago - Make Room for Baby! | YouTube


References

  1. Streeter GL. Developmental horizons in human embryos (fourth issue). A review of the histogenesis of cartilage and bone. (1949) Carnegie Instn. Wash. Publ. 583, Contrib. Embryol., 33: 149-169. PMID: 18144445
  2. Turk E, van den Heuvel MI, Benders MJ, de Heus R, Franx A, Manning JH, Hect JL, Hernandez-Andrade E, Hassan SS, Romero R, Kahn RS, Thomason ME & van den Heuvel MP. (2019). Functional connectome of the fetal brain. J. Neurosci. , , . PMID: 31685648 DOI.
  3. Khan S, Vasung L, Marami B, Rollins CK, Afacan O, Ortinau CM, Yang E, Warfield SK & Gholipour A. (2019). Fetal brain growth portrayed by a spatiotemporal diffusion tensor MRI atlas computed from in utero images. Neuroimage , 185, 593-608. PMID: 30172006 DOI.
  4. Verbruggen SW, Kainz B, Shelmerdine SC, Hajnal JV, Rutherford MA, Arthurs OJ, Phillips ATM & Nowlan NC. (2018). Stresses and strains on the human fetal skeleton during development. J R Soc Interface , 15, . PMID: 29367236 DOI.
  5. Maged A, Youssef G, Hussien A, Gaafar H, Elsherbini M, Elkomy R, Eid M, Abd El-Hamid N & Abdel-Razek AR. (2019). The role of three-dimensional ultrasonography fetal lung volume measurement in the prediction of neonatal respiratory function outcome. J. Matern. Fetal. Neonatal. Med. , 32, 660-665. PMID: 28969488 DOI.
  6. Sulak O, Ozgüner G & Malas MA. (2011). Size and location of the kidneys during the fetal period. Surg Radiol Anat , 33, 381-8. PMID: 21110022 DOI.
  7. Ishimoto H & Jaffe RB. (2011). Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit. Endocr. Rev. , 32, 317-55. PMID: 21051591 DOI.
  8. Cussen L, Scurry J, Mitropoulos G, McTigue C & Gross J. (1990). Mean organ weights of an Australian population of fetuses and infants. J Paediatr Child Health , 26, 101-3. PMID: 2361065
  9. Hansen K, Sung CJ, Huang C, Pinar H, Singer DB & Oyer CE. (2003). Reference values for second trimester fetal and neonatal organ weights and measurements. Pediatr. Dev. Pathol. , 6, 160-7. PMID: 12548377 DOI.
  10. Archie JG, Collins JS & Lebel RR. (2006). Quantitative standards for fetal and neonatal autopsy. Am. J. Clin. Pathol. , 126, 256-65. PMID: 16891202 DOI.
  11. 11.0 11.1 Westerway SC, Davison A & Cowell S. (2000). Ultrasonic fetal measurements: new Australian standards for the new millennium. Aust N Z J Obstet Gynaecol , 40, 297-302. PMID: 11065037
  12. 12.0 12.1 Locher H, de Groot JC, van Iperen L, Huisman MA, Frijns JH & Chuva de Sousa Lopes SM. (2015). Development of the stria vascularis and potassium regulation in the human fetal cochlea: Insights into hereditary sensorineural hearing loss. Dev Neurobiol , 75, 1219-40. PMID: 25663387 DOI.
  13. 13.0 13.1 13.2 13.3 Satoh T, Sakurai E, Tada H & Masuda T. (2009). Ontogeny of reticular framework of white pulp and marginal zone in human spleen: immunohistochemical studies of fetal spleens from the 17th to 40th week of gestation. Cell Tissue Res. , 336, 287-97. PMID: 19255788 DOI.
  14. 14.0 14.1 14.2 14.3 Afif A, Bouvier R, Buenerd A, Trouillas J & Mertens P. (2007). Development of the human fetal insular cortex: study of the gyration from 13 to 28 gestational weeks. Brain Struct Funct , 212, 335-46. PMID: 17962979 DOI.
  15. Kadhim HJ, Gadisseux JF & Evrard P. (1988). Topographical and cytological evolution of the glial phase during prenatal development of the human brain: histochemical and electron microscopic study. J. Neuropathol. Exp. Neurol. , 47, 166-88. PMID: 3339373
  16. 16.0 16.1 Hewer EE. The development of nerve endings in the human foetus. (1935) J Anat. 69(3):369-79. PMID 17104543
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  18. Paquette LB, Jackson HA, Tavaré CJ, Miller DA & Panigrahy A. (2009). In utero eye development documented by fetal MR imaging. AJNR Am J Neuroradiol , 30, 1787-91. PMID: 19541779 DOI.
  19. Kishimoto H, Yamada S, Kanahashi T, Yoneyama A, Imai H, Matsuda T, Takeda T, Kawai K & Suzuki S. (2016). Three-dimensional imaging of palatal muscles in the human embryo and fetus: Development of levator veli palatini and clinical importance of the lesser palatine nerve. Dev. Dyn. , 245, 123-31. PMID: 26509917 DOI.
  20. Maternal-Fetal Surgical Procedures. Walsh WF, Chescheir NC, Gillam-Krakauer M, et al. Rockville (MD): Agency for Healthcare Research and Quality (US); 2011 Apr. (Comparative Effectiveness Technical Briefs, No. 5.) Report | Comparative Effectiveness Research, Health Care
  21. Braune W. An atlas of topographical anatomy after plane sections of frozen bodies. (1877) Trans. by Edward Bellamy. Philadelphia: Lindsay and Blakiston.


Journals

Reviews

Farley D & Dudley DJ. (2009). Fetal assessment during pregnancy. Pediatr. Clin. North Am. , 56, 489-504, Table of Contents. PMID: 19501688 DOI.

Grivell RM, Wong L & Bhatia V. (2009). Regimens of fetal surveillance for impaired fetal growth. Cochrane Database Syst Rev , , CD007113. PMID: 19160321 DOI.

Articles

Search PubMed

Search Pubmed: human fetal development | fetal development | Second Trimester | Third Trimester

Carnegie Fetal

Carnegie Collection - Fetal  
Serial No. Size CRL (mm) Grade Fixative Embedding Medium Plane Thinness (µm) Stain Point Score Sex Year Notes
95 40 catalogued as CRL 40 but development suggests 50 stage. Spinal cord - Kunitomo (1920)[1] Colon - Lineback (1920)[2]
96 50 Brain venous sinuses - Streeter (1915)[3] Spinal cord - Kunitomo (1920)[1] Brain vascular - Streeter (1921)[4] Brain weight - Jenkins (1921)[5]
142 125 Spinal cord - Kunitomo (1920)[1]
145 33 Spinal cord - Kunitomo (1920)[1]
184 50 34 vertebrae, 31 spinal ganglia, Spinal cord - Kunitomo (1920)[1]
211 33 34 vertebra, 31 spinal ganglia, Spinal cord - Kunitomo (1920)[1]
217 45 Male Genital - Spaulding (1921)[6]
300 73 85 days, Bone ossification - Mall (1906)[7]
362 30 Spinal cord - Kunitomo (1920)[1]
448 52 Colon - Lineback (1920)[2]
449 36 Spinal cord - Kunitomo (1920)[1]
538
590 21 to 23 Male Genital - Spaulding (1921)[6]
607 37 Male Genital - Spaulding (1921)[6]
625 220 Temporomandibular joint - Moffatt (1957)[8]
662 80 Spinal cord - Kunitomo (1920)[1]
693 45 Male Genital - Spaulding (1921)[6]
847 58.8 Male Genital - Spaulding (1921)[6]
858 57.25 Temporomandibular joint - Moffatt (1957)[8]
922 37
928 120 Spinal cord - Kunitomo (1920)[1]
948 45 Male Genital - Spaulding (1921)[6]
972 37 34 vertebrae, 30 spinal ganglia, Spinal cord - Kunitomo (1920)[1]
1318 37 Temporomandibular joint - Moffatt (1957)[8]
1388 51 Female Genital - Spaulding (1921)[6]
1455 78.5 Temporomandibular joint - Moffatt (1957)[8]
1591 36 subcutaneous vascular plexus - Finley (1923)[9]
1656 67 34 vertebrae, Spinal cord - Kunitomo (1920)[1]
1686 40 Male Genital - Spaulding (1921)[6]
3990 49 Temporomandibular joint - Moffatt (1957)[8]
4473 43 20 Spinal cord meninges - Sensenig (1951)[10]
4475 48 20 Spinal cord meninges - Sensenig (1951)[10]
5652 49 Temporomandibular joint - Moffatt (1957)[8]
6581 75 Temporomandibular joint - Moffatt (1957)[8]
7218 80 20 um Spinal cord meninges - Sensenig (1951)[10]
1597b 47 Female Genital - Spaulding (1921)[6]
2250a 40 Female Genital - Spaulding (1921)[6]
2250b 36 Female Genital - Spaulding (1921)[6]
This table currently contains only has embryo number information.

Abbreviations

  • Size - E. is the greatest length of the embryo and Ch. is the mean diameter of the chorion.
  • Grade - total grade of the specimen and includes both its original quality and the condition of the mounted sections.
  • Embedding medium - paraffin (P) or a combination of celloidin and paraffin (C-P).
  • Fixative - formalin (Formol), alcohol and formalin (Alc, formol), Bouin (Bouin solution)
  • Stain -
  • ? - unknown or not determined.
References
  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Kunitomo K. The development and reduction of the tail and of the caudal end of the spinal cord (1920) Contrib. Embryol., Carnegie Inst. Wash. Publ. 272, 9: 163-198.
  2. 2.0 2.1 Lineback PE. Studies on the longitudinal muscle of the human colon, with special reference to the development of the taeniae. (1920) Contrib. Embryol., Carnegie Inst. Wash. Publ. 50
  3. Streeter GL. The development of the venous sinuses of the dura mater in the human embryo. (1915) Amer. J Anat.18: 145-178.
  4. Streeter GL. The developmental alterations in the vascular system of the brain of the human embryo. (1921) Contrib. Embryol., Carnegie Inst. Wash. 8:7-38.
  5. Jenkins GB. Relative weight and volume of the component parts of the brain of the human embryo at different stages of development. (1921) Contrib. Embryol., Carnegie Inst. Wash., 59: 5-54.
  6. 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 Spaulding MH. The development of the external genitalia in the human embryo. (1921) Contrib. Embryol., Carnegie Inst. Wash. Publ. 81, 13: 69 – 88.
  7. Mall FP. On ossification centers in human embryos less than one hundred days old. (1906) Amer. J Anat. 5:433-458.
  8. 8.0 8.1 8.2 8.3 8.4 8.5 8.6 Moffatt BC. The prenatal development of the human temporomandibular joint. (1957) Carnegie Instn. Wash. Publ. 611, Contrib. Embryol., 36: .
  9. Finley EB. The development of the subcutaneous vascular plexus in the head of the human embryo. (1923) Contributions to Embryology Carnegie Institution No. 71: 155-161.
  10. 10.0 10.1 10.2 Sensenig EC. The early development of the meninges of the spinal cord in human embryos. (1951) Contrib. Embryol., Carnegie Inst. Wash. Publ. 611.
Fertilization and Gestational Age - Crown-Rump Length (ultrasound
Fertilization Age
(days)
Gestational Age
GA (week.day)
Crown-Rump
Length (mm)
37 5.2 1
38 5.3 2
39 5.4 3
40 55 3
41 5.6 4
42    Week 4 6 4
43 6.1 5
44 6.2 6
45 6.3 7
46 6.4 8
47 6.5 9
48 6.6 10
49    Week 5 7 11
50 7.1 11
51 7.2 12
52 7.3 12
53 7.4 13
54 7.5 14
55 7.6 15
56    Week 6 8 17
57 8.1 18
58 8.2 19
59 8.3 20
60 8.4 21
61 8.5 22
62 8.6 22
63    Week 7 9 23
64 9.1 24
65 9.2 26
66 9.3 27
67 9.4 28
68 9.5 29
69 9.6 31
70    Week 8 10 34
71 10.1 36
72 10.2 37
73 10.3 38
74 10.4 39
75 10.5 39
76 10.6 40
77    Week 9 11 44
78 11.1 45
79 11.2 47
80 11.3 48
81 11.4 52
82 11.5 55
83 11.6 56
84    Week 10 12 57
85 12.1 58
86 12.2 60
87 12.3 61
88 12.4 63
89 12.5 64
90 12.6 65
91    Week 11 13 68
92 13.1 70
93 13.2 72
94 13.3 74
95 113.4 76
96 135 77
97 13.6 80
98    Week 12 14 81
99 14.1 84
100 14.2 85
101 14.3 86
102 14.4 87
Reference: Table data measured by ultrasound, adapted from Westerway (2015) PDF and[1]
Links: ultrasound | Fetal Development

External Links

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Cite this page: Hill, M.A. (2024, March 19) Embryology Fetal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fetal_Development

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  1. Westerway SC, Davison A & Cowell S. (2000). Ultrasonic fetal measurements: new Australian standards for the new millennium. Aust N Z J Obstet Gynaecol , 40, 297-302. PMID: 11065037