L14: Fetal Development Flashcards
What is clinical gestation
Time from a woman’s last periods first day
Or time of a woman last period day
What is the actual fertilisation compared to the clinical gestation
2 weeks before the clinical gestation
Describe what happens when the sperm and oocyte meet
Fertilisation
How does the zygote divide
By mitosis
What does the zygote form
2 cell
4 cell
8 cell
16- 32 cell
When is the cell classed as a morula
16+ cells
After the morula what forms
Blastocyst
When does the blastocyst implant into the endometrium
Implantation window
When does the implantation window appears
Mid secretory phase
At week 2 when the blastocyst is implanted what happens to it
Differentiate to form the bilaminar germ disc
What is the bilaminar germ disc made of
2 layers of
Epiblast
Hypoblast
What happens in week 3
Gastrulation
What is gastrulation
When the epiblast migrates through the primitive streak to form the ectoderm, mesoderm, endoderm (replacement of hypoblast)
At the end of week 3 what is formed
The trilaminar germ disc (ectoderm, mesoderm, endoderm) of
In week 4 what occurs
Neurlation
What does neuralation from
The neural tube
What happens to the flat trimlaminar disc
Folds to from a cylindrical embryoblast
What are the 2 types of folding that occur
- cephalo-caudal folding
- lateral folding
What does the folding allow
Organs to the correct anatomical position
What is week 3 onwards known as
The embryonic period
What happens during week 3-8 (clinical gestation 5 to 10 week)
Organogenesis
What is organogenesis
Establishment of main organs of the fetal body
What is the week 9 to 38 (clincal gestation 11 to 40) known as
Fetal period
What occurs during the fetal period
Maturation of organs and growth rather than growing new structures
What can the congenital abnormalities be
Structural
Functional- Organ is not working
Metabolic - enzyme and cellular defects
What are the causes of birth defects
Genetic
Environment
Unknown
Multifactorial: gene and environment
What can the congenital abnormalities be further classified into
Malformation
Disruption
Deformation
What is malformation
The complete and abnormal formation of a structure
What is disruption
Structures have formed then undergo morphological alterations
What is deformation
Mechanical factors
What is the most common autosomal trisomy
Down’s syndrome
What are the clinical features of Down’s syndrome
Craniofascial apperance
Single palmar creases
Wide sandle gap between toes
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
What are all mothers offered for Down syndrome
Screening only if they wish
What are the 2 ways o inheriting trisomy 21 at fertilisation
- non disjunction
- robertsonian translocation
What way of inheriting trisomy 21 is the most common
Non disjunction
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)
How does Robertsonian translocation occur
When chromosome 21 wrongly joins to another chromosome of 14,15,20,21
What does one parent have to be for robertsonian translocation to occur
Translocation carrier
What is another inheritance method if trisomy 21
Mosaichasim
What happens in mosaichasim
When some cells have normal chromosome and some have trisomy 21
When does mosaicism occur
When the zygote forms during mitosis
What is the phenotype of Down syndrome with mosaichasim
Milder because there are some normal cells
What does mosaichasim occur as a result of
Non-disjunction i.e chromosome 21 fails to separate during mitosis
When we screen for Down syndrome what does it tell us
The chance of having the condition
What does the screening test not tell us
That the baby for definite has the condition
What are the 3 screening test for Downs syndrome
Combined test
Quadruple test
NIPT
What does the combined test measure
Ultrasound nuchal translucency
What is NIPT
A blood test
What are teratogens
Agents that cause birth defects
What are the types of teratogens
Drugs Chemical Infectious agents Radiation Maternal factors Mechanical factors
Name examples of drugs that are teratogens
Alcohol Cocain Thalidomide Anti psychotics Anti convulsants Warfarin
What are the chemicals that can be teratogens
Organic mercury
Lead
What are the infectious agent that can be teratogenous
Rubella
CMV
ZIKA
What are the maternal factors that are teratogens
Pre existing diabetes (increase risk of neural tube defect)
SLE (heart block)
What are the mechanical factors that can be teratogens
Large fibroids
Oligohydromnios
Amniotic bands
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
What is neuralation
The formation of the neural tube
What are the 2 phases of neuralation
Primary neuralation
Secondary neuralation
What occurs in primary neuralation
Shaping
Middle fusion
Creates brain
Crates spinal cord
What occurs in secondary neuralation
Formation of the tail bud
What are the 3 classification of spina bifida
Occulta
Meningocele
Myelomeningocele
Which classification if the mildest form
Occulta
Which classification of Spina bifida is the most severe form
Myelomeningocele
What happens in occulta
Malformed vertebrae but is hidden with skin
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
What is myelomeningocele spina bifida
The spinal cord (neural elements) protrude through the malformed vertebra
What can the myelomeningocele cause
Paralysis and bowel problems if its in the sacral levels
What is the prevention of Spina bifida
Folic acid (pre-conception)
What has to happen to folic acid with maternal diabetes
Higher doses
Why do we give higher doses of folic acid for women with diabetes
Diabetes has a higher risk of Spina bifida
Which prominences form the fascial prominence
Frontonasal prominence Maxillary prominence (X2) Mandibular prominence (X2)
When does these fascial prominences form
In week 4
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
What can the clef lip and palate be
Unilateral lateral i.e to one side
Bilateral i.e both sides
What is a cleft palate
An effect in the palate alone and not the lip so it can be hidden
What are the 2 abdominal wall defects that can occur
Omphalocele
Gastroschisis
What is a omphalacele
Herniation of the bowel contents/viscera attached at the base of the umbilical cord
Why does omphalocele occur
Due to midgut herniation that doesn’t go back to Fetal abdomen
What does an omphalalocele appear as
A transparent sac of amnion attached to the umbilical ring
What is gastroschisis
The evisceration of fetal intestine through a paraumbilical wall defect
What is gastroschisis due to
- involution of right umbilical vein or right vitelline artery
- abnormal body wall forming
What are the main ways for detecting for congenital anomalies
genetic testing
Imaging via ultrasound
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
Which screening methods are offered by NHS for Down’s syndrome
Quadruple
Combined
What does quadruple test involve
Blood test from mother and looking for markers of: AFP, HCG, UE3, inhibin A
When can quadruple test be performed
Between 14 weeks + 2 days up to 20 weeks
What does combined test involved
Maternal blood test by looking at markers of NT, PAPPA, HCG
And
Ultrasound to look at nuchal translucency
What is the criteria for combined test be carried out
- 11 weeks + 2 days up to 14 weeks +1 day
- CRL ( 45 mm- 84mm)
What is the nuchal translucency
A fluid filled area at the back of the neck that is measured
What is NIPT (non-invasive pre-natal testing)
Blood test that you collect which contains the maternal dna and fetal dna
When you have collected the blood with the maternal dna and fetal dna what do you do
Sequence the dna and detect for trisomy
What is amniocentesis
An invasive procedure of where you collect the fluid in the amniotic sac that surrounds the fetus
What are the risk of amniocentis
Miscarriage
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
