Fetal Development

Embryology - 9 Dec 2023        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.

Historic Embryology

In 1949 the embryologist George Streeter 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 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 "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 "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 "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 "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

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. 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 | 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 "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 "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 Development Page | Play

Fetal length and weight 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

Ultrasound CRL Data

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

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 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

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

Timeline

Second Trimester Timeline 

Links: human timeline | first trimester timeline | second trimester timeline | third trimester timeline
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 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.
15		Pancreas glucagon detectable in fetal plasma. spleen Week 15 -alpha-smooth muscle actin (alpha-SMA)-positive reticulum cells scattered around the arterioles.
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. 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. gap junction cartoon neural - Cerebrum development of the periinsular sulci (week 16-17, GA 18-19 weeks) 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		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		tongue 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. 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)
19		neural week 19 neuronal migration ends and the radial glial cells that aided the migration now become transformed into astrocytes and astrocytic precursors.
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
21
22		Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present 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. neural - Cerebrum covering of the posterior insula (week 22-24, GA 24-26 weeks)
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. 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)
26		touch pacinian corpuscle well developed
	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

• 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	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
34		neural brain cortical sulcation - insular, cingular, and occipital secondary sulci present
35
36		Nail Development toenails reach digit tip Lens Development - lens growth and interocular distance plateaus after 36 weeks of gestation
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
	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 Neural

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

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

Links: Genital System Development

Fetal Renal

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	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.

Links: integumentary

Fetal Palate

Levator veli palatini skeletal muscle contacted by the lesser palatine nerve. 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.

Some examples include:

• Cardiac Malformations
• Congenital Diaphragmatic Hernia
• Myelomeningocele/Spina Bifida
• Obstructive Uropathy
• Sacrococcygeal Teratoma
• Thoracic Lesions
• Twin-Twin Transfusion Syndrome

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)

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

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

References

Journals

• Seminars in Fetal & Neonatal Medicine

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.

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) Colon - Lineback (1920)
96	50										Brain venous sinuses - Streeter (1915) Spinal cord - Kunitomo (1920) Brain vascular - Streeter (1921) Brain weight - Jenkins (1921)
142	125										Spinal cord - Kunitomo (1920)
145	33										Spinal cord - Kunitomo (1920)
184	50										34 vertebrae, 31 spinal ganglia, Spinal cord - Kunitomo (1920)
211	33										34 vertebra, 31 spinal ganglia, Spinal cord - Kunitomo (1920)
217	45								Male		Genital - Spaulding (1921)
300	73										85 days, Bone ossification - Mall (1906)
362	30										Spinal cord - Kunitomo (1920)
448	52										Colon - Lineback (1920)
449	36										Spinal cord - Kunitomo (1920)
538
590	21 to 23								Male		Genital - Spaulding (1921)
607	37								Male		Genital - Spaulding (1921)
625	220										Temporomandibular joint - Moffatt (1957)
662	80										Spinal cord - Kunitomo (1920)
693	45								Male		Genital - Spaulding (1921)
847	58.8								Male		Genital - Spaulding (1921)
858	57.25										Temporomandibular joint - Moffatt (1957)
922	37
928	120										Spinal cord - Kunitomo (1920)
948	45								Male		Genital - Spaulding (1921)
972	37										34 vertebrae, 30 spinal ganglia, Spinal cord - Kunitomo (1920)
1318	37										Temporomandibular joint - Moffatt (1957)
1388	51								Female		Genital - Spaulding (1921)
1455	78.5										Temporomandibular joint - Moffatt (1957)
1591	36										subcutaneous vascular plexus - Finley (1923)
1656	67										34 vertebrae, Spinal cord - Kunitomo (1920)
1686	40								Male		Genital - Spaulding (1921)
3990	49										Temporomandibular joint - Moffatt (1957)
4473	43					20					Spinal cord meninges - Sensenig (1951)
4475	48					20					Spinal cord meninges - Sensenig (1951)
5652	49										Temporomandibular joint - Moffatt (1957)
6581	75										Temporomandibular joint - Moffatt (1957)
7218	80					20 um					Spinal cord meninges - Sensenig (1951)
1597b	47								Female		Genital - Spaulding (1921)
2250a	40								Female		Genital - Spaulding (1921)
2250b	36								Female		Genital - Spaulding (1921)
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
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 Links: ultrasound | Fetal Development

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Cite this page: Hill, M.A. (2023, December 9) Embryology Fetal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fetal_Development

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© Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G