Fetal Growth And Devlopment Flashcards
What happens in the fetal period
• Growth and physiological maturation of the structures created during the (v much shorter) embryonic
period • Period involving preparation for the transition to independent life after birth
Whe are the pre-embryonic, embryonic and fetal period
Ss
but……..pregnancy weeks calculated from date of LMP, i.e. conception weeks +2, so term is 40 pregnancy weeks
Describ growth in development
Embryonic period is characterised by intense activity
– organogenetic period
• But absolute growth is very small
– except placenta!
• Growth & weight gain accelerate in fetal period
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Describe the patterns of growth in each state
Differential growth
• CRL (crown-rump length) increases rapidly in the pre-embryonic, embryonic & early fetal periods
• Weight gain is slow at first, then increases rapidly in mid- and late
fetal periods
– Embryo – intense morphogenesis & differentiation; little weight gain;
placental growth most significant
– Early fetus – protein deposition
– Late fetus – adipose deposition
What is Crl and how does it change
Crown rump length, ss
• Measured between 7 & 13 weeks to date the pregnancy and estimate EDD
• Scan in T1 also used to check location, number, viability
Decsribe how the body proportions of the guts changes
Body proportions change dramatically during the fetal
period
– at 9 week, the head is approx half crown-rump length – thereafter, body length & lower limb growth accelerates
Describe antenatal assessment of fetal wellbeing
• Mother
– Fetal movements
• Regular measurements of uterine expansion
– Symphysis-fundal height (Distance of palpable fungus to symphysis)
• Ultrasound scan
What si USS
Obstetric Ultrasound scan (USS)
• Safe
• Can be used early in pregnancy to calculate age
– also: rule out ectopic, number of fetuses etc.
• Routinely carried out at ~20 weeks
– Assess fetal growth
– Fetal anomalies
Really good to asses overal growth o structures and to assess anomalies
How is fetal age estimated
• LMP
– Prone to inaccuracy Implantation bleeding can cause ppl to htink theyve had a menstruatedl period
• Developmental criteria
– Allow accurate estimation of fetal age
What is the biparietal diameter
• The distance between the parietal bones of the fetal skull
• Used in combination with other measurements to date pregnancies in T2 &
T3
What is ac and fl
Abdominal circumference & femur length
• AC & FL used in combination with BPD for dating and growth monitoring
• Also useful for anomaly detection
Able to look at facem spinal cord, stomach, abdominal circumference
What is 3- or 4- d uss
• New wave of obstetric ultrasonography
• Not currently replacing standard USS
– Complimentary tool
Moving 3d scan is now widely available
How are birth weights classified
• 3500 g is considered average • < 2500 g suggests growth restriction • > 4500 g is macrosomia – maternal diabetes • Many factors influence birth weight, not all pathological
What is teh important of accurate dating
• Babies can have low birth-weight because
– they are premature
OR
– they are constitutionally small eg other is small
OR
– they have suffered growth restriction
• associated with neonatal morbidity & mortality - antenatal assents are al about detecting abnormalities
When do the lungs develop and what is developed in the embryonic stage
• The lungs develop relatively late
– Embryonic development creates only the bronchopulmonary tree
– Functional specialisation occurs in the fetal period
– Major implications for pre-term survival
What ar ethe restaurants diverticulitis and tracheosopahgeal septum
Respiratory diverticulitis is endoderm derived. Tracheosphageal septum is tissue which develops between GI tract rom trachea
Describe teh pseudoglandular stage
Weeks 8 – 16: Pseudoglandular stage
• Duct system begins to form within the bronchopulmonary
segments created during the
embryonic period
– bronchioles
Epithelial lined tubes which continue to branch
Decsribe teh canalicular stage
Weeks 16 – 26: canalicular stage
• Formation of respiratory bronchioles
– Budding from bronchioles formed
during the pseudoglandular stage
What si the terminal sac stage
Weeks 26 – term: terminal sac stage • Terminal sacs begin to bud from the respiratory bronchioles • Differentiation of – Type I & Type II pneumocytes • surfactant
Describe the lunges during t2 and t3
• Gas exchange conducted at placenta, but lungs must be prepared to assume full burden at birth • “breathing” movements
– conditioning of the respiratory musculature - “use it or lose it”
• Fluid filled
– crucial for normal lung development
Amniotic fluid is drawin into developing resp tract - washing th extract - exchange the fluid in and out through breathing movement. Signalling molecules then promote alvelar development. Mutually beneficial arrangement
What are implications for re-term survival
• Threshold of viability
– “Cannot be continually pushed back since there is a limit beyond which
the lungs will not be sufficiently developed to sustain life”
• BMA briefing document on fetal viability
• Viability is only a possibility once the lungs have entered the
terminal sac stage of development
– i.e. > 24 weeks - Fetus is not viable if it does not have alveoli
What is respiratory distress yndomr
• Often affects infants born pre-maturely
• Insufficient surfactant production
Pneumocytes might not be numerous enough to produce sufficient surfactant - development of type 2 pneumocytes lags
• If pre-term delivery is unavoidable or inevitable
– glucocorticoid treatment (of the mother)
– increases surfactant production in fetus
Sometime need to deliver early eg pre-eclampsia. Treat other with glucocorticoids which triggers a response in fetal lungs - increases surfactant prodution -
When is the definitive heart rate achieved
• The fetal cardiovascular system is arranged to ensure oxygenated blood collected by umbilical vein at the placenta is circulated around the fetus
• The definitive fetal H/R is achieved at around 15 weeks
– fetal bradycardia is associated with fetal demise
Wat si the fetal kidney function
- Fetal kidney function begins in week 10
- Fetal urine is a major contributor to amniotic fluid volume
- Fetal kidney function is not necessary for survival in utero (bc of placenta), but without it there is oligohydramnios - smaller than normal volume of amniotic fluid
Define oligohydramnios and polyhydrammios
• Oligohydramnios
– Too little
– Placental insufficiency, fetal renal impairment
• Polyhydramnios
– Too much
– Fetal abnormality – e.g. inability to swallow - accumulation outside
Might be a Robles with tracheosopacheal septum
Might be a neurological abnormality so derange coordination
Describe teh development of the nervous system
• Nervous system is first to begin development and last to finish
• Corticospinal tracts required for coordinated voluntary movements begin to form in the 4th month
• Myelination of brain only begins in 9th month
– e.g. corticospinal tract myelination incomplete at birth, as evidence by
increasing infant mobility in the 1st year
Huma babies relatively immature compared to most other mammals
Describe teh development of the sensory and moos systems
• No movement until the 8th week • Thereafter a large repertoire of movements develop – “practising” for post-natal life • e.g. suckling, breathing Ss
What is quickening
Implications
• “quickening”
– maternal awareness of fetal movements from 17 weeks onwards - earlier if have been pregnant before
– low cost, simple method of ante partum fetal surveillance
– reveal those fetuses requiring follow up
Descirb ethe development of the lugs and brain in terms of timing
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