Fetal Development
Embryology - 5 Jun 2024 Expand to Translate |
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Introduction
<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.
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Changing fetal proportions, not size growth. | 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 | |||
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- 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
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More recent papers |
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This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Fetal Development <pubmed limit=5>Fetal+Development</pubmed> |
Reading
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Fetal Development - Length - Weight | |||
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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
- 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.
Then look in detail at the head development in a 12 week fetus showing both forms of ossification in the skull.
Third Trimester
Third trimester Crown-Rump Length
- 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
Fetal Fissure Development | Timeline Neural Development |
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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
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
Fetal Genital
- ovary and testis development
- external genital development
- testis descent
- Links: Genital System Development
Fetal Renal
- 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:
- Vesicle (V) stage (13-19 weeks, second trimester)
- S-shaped body (S) stage ( 20-24 weeks, second trimester)
- Capillary loop (C) stage (25-29 weeks, third trimester)
- Maturation (M) stage (infants aged 1-6 months, neonatal and postnatal)
- Links: Fetal Renal | Renal System Development
Fetal Gastrointestinal
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.
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:
- Cardiac Malformations
- Congenital Diaphragmatic Hernia
- Myelomeningocele/Spina Bifida
- Obstructive Uropathy
- Sacrococcygeal Teratoma
- Thoracic Lesions
- Twin-Twin Transfusion Syndrome
References
- ↑ <pubmed>21110022</pubmed>
- ↑ <pubmed>21051591</pubmed>
- ↑ 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
- ↑ 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.
- ↑ Archie JG, Collins JS & Lebel RR. (2006). Quantitative standards for fetal and neonatal autopsy. Am. J. Clin. Pathol. , 126, 256-65. PMID: 16891202 DOI.
- ↑ 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, June 5) Embryology Fetal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fetal_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G