L13 - Foetal Development Flashcards
What is the difference between a malformation, disruption and deformation?
- Malformation refers to abnormal formation of a structure
- Disruption refers to alterations to an already-formed structure due to an intrinsic destructive process
- Deformation refers to alterations to an already-formed structure due to an extrinsic mechanical factor
What is the difference between a syndrome, association and sequence?
- A syndrome is a group of abnormalities which tend to occur together with a specific known cause
- An association is a group of abnormalities which tend to occur together without a specific known cause
- A sequence is a cascade of abnormalities
What are the features of Down’s syndrome?
1 - Congenital heart defects
2 - Duodenal atresia (closure of the duodenum)
3 - Learning difficulties
4 - Early onset Alzheimer’s
5 - Single palmar creases & wide sandal gap
6 - Hypotonia
How does the trisomy occur in Down’s syndrome?
- 94% of trisomy 21 is caused by nondisjunction
- 6% of trisomy 21 is causes by robertsonian translocation
Which agents are teratogenic?
- Drugs – e.g. alcohol, cocaine, thalidomide, ACEIs, warfarin, antipsychotics, anticonvulsants
- Environmental chemicals – e.g. organic mercury, lead
- Infectious agents – e.g. rubella, CMV
- Radiation
- Maternal factors – e.g. SLE, poorly controlled pre-existing DM
- Mechanical factors – e.g. malformed uterus, oligohydramnios, amniotic band
How do teratogens affect foetal development at different points in development?
- Insult before embryonic period (<2wks) -> no effect or miscarriage
- Organogenesis period (wks 3-8) most sensitive to malformation & exposure to teratogens will typically lead to birth defects (different organ systems will have different periods of peak sensitivity)
- Exposure during foetogenesis period (wks 9-38) -> won’t usually lead to birth defects, but main effect on growth & functional maturation
How does spina bifida arise?
Caused by a defect in the closure of the neural tube
List the types of spina bifida.
What is the difference between each type?
- Occulta – defect in bone surrounding spinal cord -> doesn’t normally cause any functional abnormality
- Meningocele – herniation of meninges & CSF out of spinal column
- Myelomeningocele – additional herniation of spinal cord
What are the lemon and banana signs?
Changes in the brain & spine of foetus due to spina bifida that are detected on ultrasound:
- Lemon sign - concavity of frontal bones
- Banana sign - abnormally bent cerebellum
How is spina bifida prevented?
Folic acid
How does cleft lip occur during development?
- Results from failure of maxillary process & medial nasal clefts to form upper lip & fusion of palatal shelves to form palate
- Can be unilateral or bilateral, or may be hidden due to effect on palate alone
What is an omphalocele?
The herniation of abdominal contents into the umbilical cord -> transparent sac of amnion attached to umbilical ring containing herniated viscera
What is gastroschisis?
The evisceration of foetal intestine through paraumbilical wall defect
What is a nuchal translucency?
Thickness of fluid pad behind baby’s head measured -> increased thickness + blood markers increases likelihood of Down’s + cardiac problems
List 7 methods of prevention of pre-conception birth defects.
1 - Maternal vaccination vs viruses e.g. rubella
2 - Avoidance of teratogenic substances
3 - Folic acid to prevent neural tube defects
4 - Improved maternal nutrition e.g. iodine
5 - Optimised disease control e.g. DM
6 - Reducing maternal age
7 - Prenatal genetic testing
