L14: Fetal Development Flashcards
1
Q
What is clinical gestation
A
Time from a woman’s last periods first day
Or time of a woman last period day
2
Q
What is the actual fertilisation compared to the clinical gestation
A
2 weeks before the clinical gestation
3
Q
Describe what happens when the sperm and oocyte meet
A
Fertilisation
4
Q
How does the zygote divide
A
By mitosis
5
Q
What does the zygote form
A
2 cell
4 cell
8 cell
16- 32 cell
6
Q
When is the cell classed as a morula
A
16+ cells
7
Q
After the morula what forms
A
Blastocyst
8
Q
When does the blastocyst implant into the endometrium
A
Implantation window
9
Q
When does the implantation window appears
A
Mid secretory phase
10
Q
At week 2 when the blastocyst is implanted what happens to it
A
Differentiate to form the bilaminar germ disc
11
Q
What is the bilaminar germ disc made of
A
2 layers of
Epiblast
Hypoblast
12
Q
What happens in week 3
A
Gastrulation
13
Q
What is gastrulation
A
When the epiblast migrates through the primitive streak to form the ectoderm, mesoderm, endoderm (replacement of hypoblast)
14
Q
At the end of week 3 what is formed
A
The trilaminar germ disc (ectoderm, mesoderm, endoderm) of
15
Q
In week 4 what occurs
A
Neurlation
16
Q
What does neuralation from
A
The neural tube
17
Q
What happens to the flat trimlaminar disc
A
Folds to from a cylindrical embryoblast
18
Q
What are the 2 types of folding that occur
A
- cephalo-caudal folding
- lateral folding
19
Q
What does the folding allow
A
Organs to the correct anatomical position
20
Q
What is week 3 onwards known as
A
The embryonic period
21
Q
What happens during week 3-8 (clinical gestation 5 to 10 week)
A
Organogenesis
22
Q
What is organogenesis
A
Establishment of main organs of the fetal body
23
Q
What is the week 9 to 38 (clincal gestation 11 to 40) known as
A
Fetal period
24
Q
What occurs during the fetal period
A
Maturation of organs and growth rather than growing new structures
25
What can the congenital abnormalities be
Structural
Functional- Organ is not working
Metabolic - enzyme and cellular defects
26
What are the causes of birth defects
Genetic
Environment
Unknown
Multifactorial: gene and environment
27
What can the congenital abnormalities be further classified into
Malformation
Disruption
Deformation
28
What is malformation
The complete and abnormal formation of a structure
29
What is disruption
Structures have formed then undergo morphological alterations
30
What is deformation
Mechanical factors
31
What is the most common autosomal trisomy
Down’s syndrome
32
What are the clinical features of Down’s syndrome
Craniofascial apperance
Single palmar creases
Wide sandle gap between toes
33
If a Down syndrome baby’s is born what do we need to counsel parents about
That the baby can have:
- hypotonia
- congenital heart defects
- duodenal atresia and bowel is closed
- learning difficulty
- early set Alzheimer’s
34
What are all mothers offered for Down syndrome
Screening only if they wish
35
What are the 2 ways o inheriting trisomy 21 at fertilisation
- non disjunction
| - robertsonian translocation
36
What way of inheriting trisomy 21 is the most common
Non disjunction
37
How does non disjunction occur in trisomy 21
Chromosome 21 from one of the parents cell fails to separate at meiosis so one gamete has 2 chromosome 21s and at fertilisation it gives rise to 3 chromosome 21s ( 1 from father and 2 from mother)
38
How does Robertsonian translocation occur
When chromosome 21 wrongly joins to another chromosome of 14,15,20,21
39
What does one parent have to be for robertsonian translocation to occur
Translocation carrier
40
What is another inheritance method if trisomy 21
Mosaichasim
41
What happens in mosaichasim
When some cells have normal chromosome and some have trisomy 21
42
When does mosaicism occur
When the zygote forms during mitosis
43
What is the phenotype of Down syndrome with mosaichasim
Milder because there are some normal cells
44
What does mosaichasim occur as a result of
Non-disjunction i.e chromosome 21 fails to separate during mitosis
45
When we screen for Down syndrome what does it tell us
The chance of having the condition
46
What does the screening test not tell us
That the baby for definite has the condition
47
What are the 3 screening test for Downs syndrome
Combined test
Quadruple test
NIPT
48
What does the combined test measure
Ultrasound nuchal translucency
49
What is NIPT
A blood test
50
What are teratogens
Agents that cause birth defects
51
What are the types of teratogens
```
Drugs
Chemical
Infectious agents
Radiation
Maternal factors
Mechanical factors
```
52
Name examples of drugs that are teratogens
```
Alcohol
Cocain
Thalidomide
Anti psychotics
Anti convulsants
Warfarin
```
53
What are the chemicals that can be teratogens
Organic mercury
| Lead
54
What are the infectious agent that can be teratogenous
Rubella
CMV
ZIKA
55
What are the maternal factors that are teratogens
Pre existing diabetes (increase risk of neural tube defect)
| SLE (heart block)
56
What are the mechanical factors that can be teratogens
Large fibroids
Oligohydromnios
Amniotic bands
57
Why is timing of the teratogens important
If:
- prior to post fertilisation week 2: miscarriage
- week 3 to 8: affect organs
- week 9 to 38: affects growth and maturation
58
What is neuralation
The formation of the neural tube
59
What are the 2 phases of neuralation
Primary neuralation
| Secondary neuralation
60
What occurs in primary neuralation
Shaping
Middle fusion
Creates brain
Crates spinal cord
61
What occurs in secondary neuralation
Formation of the tail bud
62
What are the 3 classification of spina bifida
Occulta
Meningocele
Myelomeningocele
63
Which classification if the mildest form
Occulta
64
Which classification of Spina bifida is the most severe form
Myelomeningocele
65
What happens in occulta
Malformed vertebrae but is hidden with skin
66
What occurs in meningocele Spina bifida
You have a malformed vertebrae and meninges and spinal cord fluid protrudes out through the malformed vertebrae.
Does not contain neural elements
67
What is myelomeningocele spina bifida
The spinal cord (neural elements) protrude through the malformed vertebra
68
What can the myelomeningocele cause
Paralysis and bowel problems if its in the sacral levels
69
What is the prevention of Spina bifida
Folic acid (pre-conception)
70
What has to happen to folic acid with maternal diabetes
Higher doses
71
Why do we give higher doses of folic acid for women with diabetes
Diabetes has a higher risk of Spina bifida
72
Which prominences form the fascial prominence
```
Frontonasal prominence
Maxillary prominence (X2)
Mandibular prominence (X2)
```
73
When does these fascial prominences form
In week 4
74
What does a cleft lip and palate form as a result of
Failure of fusion of maxillary process ad medial nasal clefts that from the upper lip
Failure of fusion of the palatal shelves to from the palate
75
What can the clef lip and palate be
Unilateral lateral i.e to one side
| Bilateral i.e both sides
76
What is a cleft palate
An effect in the palate alone and not the lip so it can be hidden
77
What are the 2 abdominal wall defects that can occur
Omphalocele
| Gastroschisis
78
What is a omphalacele
Herniation of the bowel contents/viscera attached at the base of the umbilical cord
79
Why does omphalocele occur
Due to midgut herniation that doesn’t go back to Fetal abdomen
80
What does an omphalalocele appear as
A transparent sac of amnion attached to the umbilical ring
81
What is gastroschisis
The evisceration of fetal intestine through a paraumbilical wall defect
82
What is gastroschisis due to
- involution of right umbilical vein or right vitelline artery
- abnormal body wall forming
83
What are the main ways for detecting for congenital anomalies
genetic testing
| Imaging via ultrasound
84
What methods involve genetic testing
- screening for Down’s syndrome
- pre-implantation genetic diagnosis if mother had a previous pregnancy affected
- invasive testing : chronic villious testing, amniocentesis
- non invasive: maternal blood
85
Which screening methods are offered by NHS for Down’s syndrome
Quadruple
| Combined
86
What does quadruple test involve
Blood test from mother and looking for markers of: AFP, HCG, UE3, inhibin A
87
When can quadruple test be performed
Between 14 weeks + 2 days up to 20 weeks
88
What does combined test involved
Maternal blood test by looking at markers of NT, PAPPA, HCG
And
Ultrasound to look at nuchal translucency
89
What is the criteria for combined test be carried out
- 11 weeks + 2 days up to 14 weeks +1 day
| - CRL ( 45 mm- 84mm)
90
What is the nuchal translucency
A fluid filled area at the back of the neck that is measured
91
What is NIPT (non-invasive pre-natal testing)
Blood test that you collect which contains the maternal dna and fetal dna
92
When you have collected the blood with the maternal dna and fetal dna what do you do
Sequence the dna and detect for trisomy
93
What is amniocentesis
An invasive procedure of where you collect the fluid in the amniotic sac that surrounds the fetus
94
What are the risk of amniocentis
Miscarriage
95
How can we avoid birth defects pre-conception
- vaccination for rubella
- avoid teratogenic drugs
- folic acid to reduce neural tube defects
- vitamin D
- decrease iodine
- optimise disease control such as diabetes
- reduce BMI
