Fetal Development: Difference between revisions

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Revision as of 17:07, 12 May 2016

Embryology - 29 Mar 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
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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.


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)
  • Size and location of the kidneys during the fetal period[1] "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[2] "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)
More recent papers
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  • The displayed list of references do not reflect any editorial selection of material based on content or relevance.
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References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

More? References | Discussion Page | Journal Searches | 2019 References | 2020 References

Search term: Fetal Development

<pubmed limit=5>Fetal+Development</pubmed>

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 [3][4][5]

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.

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

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.


Links: Third Trimester

Fetal Head Growth


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

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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
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 System Development

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 Development | Gastrointestinal Tract Development

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.[6]

Some examples include:


References

  1. <pubmed>21110022</pubmed>
  2. <pubmed>21051591</pubmed>
  3. 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
  4. 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.
  5. Archie JG, Collins JS & Lebel RR. (2006). Quantitative standards for fetal and neonatal autopsy. Am. J. Clin. Pathol. , 126, 256-65. PMID: 16891202 DOI.
  6. 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


Journals

Reviews

<pubmed>19501688</pubmed> <pubmed>19160321</pubmed>

Articles

Search PubMed

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



Glossary Links

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Cite this page: Hill, M.A. (2024, March 29) Embryology Fetal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fetal_Development

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G