S7) Foetal Growth and Development Flashcards Preview

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Flashcards in S7) Foetal Growth and Development Deck (42)
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What is the foetal period and what happens during this?

- The foetal period is the period involving preparation for the transition to independent life after birth

- Growth and physiological maturation of the structures created during the embryonic period occurs



What characterises the embryonic period?

Embryonic period is characterised by intense activity (organogenetic period) but absolute growth is very small 


What is crown-rump length?

Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump)


Describe the differential growth observed in the crown-rump length

CRL increases rapidly in the pre-embryonic, embryonic & early fetal periods 


Describe how weight gain varies in the different foetal periods 

Embryo – intense morphogenesis & differentiation; little weight gain; placental growth most significant

- Early foetus – protein deposition

Late foetus – adipose deposition 


Explain how body proportions change during the foetal period 

- 9 weeks, the head is approx half crown-rump length

- Thereafter, body length & lower limb growth accelerates 


Identify and describe 3 different ways of assessing foetal well-being

Mother – foetal movements

- Regular measurements of uterine expansion – symphysis-fundal height

- Ultrasound scan 


Obstetric ultrasound scan (USS) is routinely carried out at ~20 weeks. 

Identify 5 advantages of this

- Safe

- Can be used early in pregnancy to calculate age

- Rules out ectopic pregnancy

- Indicates number of foetuses

- Assess foetal growth and anomalies 


Identify and describe 2 different ways of estimating foetal age

- Last menstrual period (LMP) – prone to inaccuracy

- Developmental criteria – allows accurate estimation of fetal age 


Why and when do we measure crown-rump length?

Measured between 7 & 13 weeks to date the pregnancy and estimate EDD 


What is biparietal diameter and when is it used?

- Biparietal diameter is the distance between the parietal bones of the fetal skull

- Used in combination with other measurements to date pregnancies in T2 & T3 


When is abdominal circumference and femur length used?

- AC & FL used in combination with BPD for dating and growth monitoring

- Useful for anomaly detection 


How do we classify birth weights?

- Average: 3500 g

- Growth restriction: < 2500 g 

- Macrosomia: > 4500 g (maternal diabetes)


Provide 3 possible reasons for low-birth weight

- They are premature

- They are constitutionally small

- They have suffered growth restriction (associated with neonatal morbidity & mortality)


The lungs develop relatively late.

Why is this?

- Embryonic development creates only the bronchopulmonary tree

- Functional specialisation occurs in the foetal period 


Identify the different stages in the development of the respiratory system

Weeks 8 – 16: pseudoglandular stage 

Weeks 16 – 26: canalicular stage 

Weeks 26 – term: terminal sac stage 


Describe the pseudoglandular stage in lung development

- Duct system begins to form within the bronchopulmonary segments created during the embryonic period

- Forms bronchioles 


Describe the canulicular stage in lung development

Formation of respiratory bronchioles through budding from bronchioles formed during the pseudoglandular stage 


Describe the terminal sac stage in lung development

Terminal sacs begin to bud from the respiratory bronchioles

- Type I & Type II pneumocytes differentiate

- Surfactant is produced



Gas exchange is conducted at placenta, but lungs must be prepared to assume full burden at birth.

How does this happen in T2 and T3?

- “Breathing” movements condition of the respiratory musculature

- Fluid filled spaces crucial for normal lung development 


Discuss the threshold for viability in terms of pre-term survival

Viability is only a possibility once the lungs have entered the terminal sac stage of development (> 24 weeks)


Respiratory distress syndrome often affects infants born pre-maturely and involves insufficient surfactant production.

How can this be treated?

Glucocorticoid treatment (of the mother) increases surfactant production in foetus if preterm delivery is inevitable/unavoidable


When is the definitive foetal heart rate determined?

- The definitive fetal HR is achieved at around 15 weeks 

- Foetal bradycardia is associated with fetal demise 


Describe the development of the urinary system in the foetus and the importance of such

- Foetal kidney function begins in week 10

- Foetal urine is a major contributor to amniotic fluid volume 


Describe the variations in amniotic fluid volume

Oligohydramnios: too little amniotic fluid due to placental insufficiency or fetal renal impairment

- Polyhydramnios: too much amniotic fluid due to foetal abnormality e.g. inability to swallow 


The nervous system is first to begin development and last to finish.

Briefly outline its development

Corticospinal tracts required for coordinated voluntary movements to begin to form in the 4th month

- Myelination of brain only begins in 9th month 


Outline the development of sensory and motor systems

- No movement until the 8th week

- Thereafter a large repertoire of movements develop to “practise” for post-natal life e.g. suckling, breathing 


What is "quickening" and what is its the benefit?

- Quickening is the maternal awareness of fetal movements from 17 weeks onwards

- It is a low cost, simple method of ante-partum fetal surveillance and reveals those foetuses requiring follow-up 


In terms of chronology, compare and contrast the development of the brain and lungs


Identify 3 benefits of transvaginal ultrasound

- Check that conceptus implanted in correct place

- Rule out ectopic pregnancy

- Check for multiple foetuses