Foetal development and growth Flashcards
What happens in week 1 (clinical gestation week 3)?
Sperm and ovum join = fertilisation
Forms into a morula then a blastocyst which then implants into the endometrial wall
What happens in week 2 (clinical gestation week 4)?
Bilaminar germ discs form = epiblast/hypoblast
What happens in week 3 (clinical gestation week 5)?
Trilaminar germ disc forms
- Gastrulation
- Ectoderm/Mesoderm/Endoderm - from these 3 layers all the rest of the body can form
- Neurulation - by end of 4th week
When does folding of the embryonic disc occur and what ways does it fold?
Flat trilaminar disc to cylindrical embryo
- cephalo-caudal folding
- lateral folding
What happens in the embryonic period?
Organogenesis
Establishment of main organ systems
Post-fertilisation week 3-8 (clinical gestation 5-10 weeks)
What happens in the foetal period?
Maturation and growth of tissues and organs
Post-fertilisation weeks 9-38 (clinical gestation 11-40 weeks)
What are the different types of birth defects?
Developmental disorders present at birth Types: - structural = congenital anomaly - functional = organ dysfunction - metabolic = enzyme/cellular defect
What are the causes of birth defects?
Genetic
Environmental
Multi-factorial inheritance
- interaction between genetic constitution and environmental factors
What are some different causes of congenital anomalies?
Malformation
- incomplete or abnormal formation of structure
- complete of partial absence of a structure
- alteration of its normal configuration
Disruption
- morphological alterations of already formed structure
- destructive process e.g. amniotic bands
Deformation
- mechanical factors e.g. positional talipes
What are some different causes of chromosomal/genetic issues?
Multi-organ involvement - usually lethal /significant defect
Syndromes
- group of anomalies with a specific known cause eg. Down’s Syndrome
Association
- abnormalities which tend to occur together but the cause is not determined e.g. CHARGE
Sequence
- when a defect leads to a cascade of further abnormalities e.g. potters sequence - baby doesn’t have any kidneys and this subsequently means no urine is produced, leading to no amniotic fluid and this leads to multiple abnormalities
What are the clinical features of Down’s syndrome?
- craniofacial appearance = flat nasal bridge, upslanted palpebral fissures, epicanthic folds, brushfield spots
- single palmar crease and wide sandal gap
- Hypotonia
- Congenital heart defects - 40%
- Duodenal atresia
- variable learning difficulties
- Alzheimer’s / Malignancy
What are the different genetic causes of trisomy 21?
Non-disjunction - 94-95%
Robertsonian translocation
Mosaicism
What are the determining factors of a teratogenic birth defects?
Timing
Dosage
Genetic constitution of the embryo
What are some different types of teratogens?
Drugs - alcohol, cocaine, thalidomide, anticonvulsants, antipsychotics
Environmental factors - organic mercury, lead
Infectious agents - rubella, CMV
Radiation - high levels of ionising radiation
Maternal factors - SLE, poorly controlled pre-existing DM
Mechanical factors - malformed uterus, oligohydramnios, amniotic band
Based upon the timing of the foetus’ life, what impact does insult to teratogens have on the foetus?
Prior to post-fertilisation week 2
- either a miscarriage or no effect
Organogenesis period (weeks 3-8)
- period of greatest sensitivity to malformation
- different organ systems have different periods of peak sensitivity
- leading to birth defect
Foetogenesis period (weeks 9-38)
- main effect on growth and functional maturation
- usually not leading to birth defect
What is omphalocele?
Abdominal wall defect
- transparent sac of amnion attached to umbilical ring containing herniated viscera
1 in 4,000 births
Persistence of embryonic midgut herniation
60% associated with other abnormalities
20% chromosomal abnormalities e.g. Edwards
What is gastroschisis?
Abdominal wall defect
- Evisceration of foetal intestine through a paraumbilical wall defect - to the R of the umbilicus
- 1 in 4,000 births but increasing
- Possible origins: involution of right umbilical vein or right viteline artery, abnormal body wall folding
- associated with young mums, smoking and drug use
- good prognosis after surgical correction
How can you detect for congenital anomalies ?
Genetic testing
- screening e.g. down’s syndrome
- pre-implantation genetic diagnosis
- invasive testing and non-invasive testing: single gene disorders, chromosomal abnormalities
Imaging
- Detailed foetal anomaly scan for structural anomalies - week 20
What are the 2 examples of non-invasive prenatal testing (NIPT) for Down’s syndrome and how effective are they?
Shotgun = 98.6-100% detection rate
- false positives= 0.2-2.1%
- No results rate = 0.8 -3.9%
Targeted = 99.5-100% detection rate
- false positives = 0-0.3%
- no results rate = 0.8-4.6%
What is foetoscopy?
foetoscopic laser ablation for foeto-foetal transfusion syndrome
What is foetal blood sampling used for?
Foetal haemoglobin for anaemia
Foetal infection serology
Foetal blood transfusion
What is encompassed in chorionic villus sampling?
Chromosome/microarray and DNA analysis
Enzyme analysis of inborn error of metabolism
What is pre-implantation genetic diagnosis ?
In-vitro fertilisation allows genetic analysis of cells from a developing embryo before transfer to the uterus
What is non-invasive genetic diagnosis?
Free foetal DNA obtained from maternal blood for identification of foetal gender and rhesus status
