Lecture 19- Foetal development

Question 1

The fetal period

Answer 1

• occurs after the embryonic period
• Growth and physiological maturation of structures created during the (v much shorter) embryonic period
• Period involving preparing for the transition to independent living after birth

Question 2

pre-embyonic period

Answer 2

between weeks 1-2 (blastocyst)

Question 3

embyronic period

Answer 3

WEEK 3- 9

Question 4

fetal period

Answer 4

weeks 9-38

Question 5

pregnancy weeks calculated form of

Answer 5

last menstrual period

i.e. conception weeks +2, so derm is 40 weeks

Question 6

Pattern of growth during embryonic development

Answer 6

• Embryonic period is characterised by intense activity–>organogenetic period
• But absolute growth is very small
  
  • Except placenta!
  • Growth and weight gain accelerate in fetal period

Question 7

what is used to assess gorwth

Answer 7

crown-rump lenght (CRL) and weight

Question 8

• Crown-rump length (CRL)

Answer 8

increases rapidly in pre-embryonic, embryonic and early fetal periods

Question 9

• Weight gain during development

Answer 9

• slow at first, then increases rapidly in mid- and late fetal periods
  
  • Embryo- intense morphogenesis and differentiation, little wight gain, placental growth is most significant
  • Early fetus- protein deposition
  • Late fetus- adipose deposition

Question 10

Antenatal assessment of fetal wellbeing

Answer 10

• Fetal movements
  
  • Asking the mother if she has noticed changes in movement
• Regular measurements of uterine expansion
  
  • Symphysis-fundal height
• Ultrasound scan

Question 11

Obstetric ultrasound scan (USS)

Answer 11

• Safe
• Can be used early in pregnancy to calculate age
  
  • Also to rule out ectopic, the number of foetuses’ etc
• Routinely carried out at 20 weeks
  
  • Assess fetal growth
  • Fetal anomalies

Question 12

Estimation of fetal age based on 2 factors

Answer 12

• LMP- last menstrual period
  
  • Prone to inaccuracy
• Developmental criteria
  
  • Allow accurate estimation of fetal age
    
    • Size e.g. CRL
    • Growth curves

Question 13

estimation of fetal age in trimester 1

Answer 13

Crown rump length

• Highly accurate when measuring between 7 and 13 weeks to date the pregnancy and estimate EDD
• Scan in T1 to check location, number and viability (heart beat)

Question 14

estimation of fetal age in the 2 and 3 trimester

Answer 14

Biparietal diameter

• Distance between the parietal bones of the fetal skull
• Used in combination with other measurements to date pregnancy’s in T3 and T4

Abdominal cirucmferene and femur length

Question 15

3- or 4-D USS

Answer 15

• New wave of obstetric ultrasonography
• Not currently replacing standard USS

Great at detecting potential congenital anomalies

Question 16

classification of birth weights

Answer 16

• 3500g considered average
• <2500g suggests growth restriction
• >4500g is marcosomnia (maternal diabetes)

Question 17

The importance of accurate dating

• Babies can have low birth-weight because

Answer 17

• They are premature
• Constitutionally small
  
  • Small mother= small baby
• Suffered growth restriction (USS designed to pick this up)
  
  • Neonatal morbidity and mortality

Question 18

development of the respiratory system: the lungs develop relatively

Answer 18

late

• Not needed during embryonic or foetal life

Question 19

in embryonic development which parts of the repsiratory system are created

Answer 19

bronchopulmonary tree

Question 20

in the fetal period which parts of the respiratory system are developed

Answer 20

• Functional specialisation occurs in the fetal period
• Major implications for pre-term surivival

Question 21

lungs are derived from

Answer 21

primitive gut tube (same as endoderm as GI tract)

Question 22

respiratory system development: Week 8-16

Answer 22

pseudo glandular stage

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

Question 23

respiratory system development: week 16- 28

Answer 23

• Formation of respiratory bronchioles
• Budding from bronchioles formed during the pseudoglandular stage

Question 24

respiratory system development: Weeks 26- term

Answer 24

• Terminal sac begins to bud from resp bronchioles
• Differentiation of Type I and II penuomocytes

Question 25

**The lungs during T2 and T3**

Answer 25

* Gas exchange conducted at the placenta but lungs must be prepared to assume full burden at birth * Breathing movements to practice during foetal development * Conditioning of the respiratory musculature * Breathing movement means amniotic fluid goes into the lungs à crucial for normal developmentà promotes differentiation

Question 26

viability depends massively on the

Answer 26

how far the resp system is developed

Question 27

* Viability is only possibility once the lungs have entered the

Answer 27

* terminal sac stage of development \>24 weeks * Can have abortion up till then

Question 28

**Respiratory distress syndrome**

Answer 28

* Insufficient surfactant production by type 2 pneumocytes * If pre-term is unavoidable or inevitable * Glucocorticoid treatment (of the mother) * Increases surfactant production in fetus

Question 29

respiratory distress syndrome pathophysiology

Answer 29

The primary cause of RDS is inadequate pulmonary surfactant. The structurally immature and surfactant-deficient lung has ↓ compliance and a tendency to atelectasis; other factors in preterm infants that ↑ the risk of atelectasis are decreased alveolar radius and weak chest wall

Question 30

**The cardiovascular system** *

Answer 30

* Fetal cardiovascular system is arranged to ensure oxygenated blood collected by umbilical veins at the placenta and is circulated around the fetus * Definitive fetal H/R is achieved at around 15 weeks

Question 31

Fetal bradycardia associated with

Answer 31

fetal demise

Question 32

fetal kidney function begins in

Answer 32

week 10

Question 34

* Fetal urine major contributor of

Answer 34

* amniotic fluid volume

Question 35

oligohydramnios

Answer 35

too little amniotic fluid due to: * placental insufficiency--\> not enough blood provided to be filtered by the kidney * fetal renal impairment

Question 36

polyhydramnios

Answer 36

too much amniotic fluid due to * fetal abnormality such as inability to swallow

Question 37

Fetal kidney function not necessary for survival in utero, but without it there is

Answer 37

oligohydramnios (lower than normal amniotic fluid)

Question 38

the nervous system is the

Answer 38

* First to begin development and last to finish

Question 39

nervous system development in the foetal period

Answer 39

* Corticospinal tracts required for coordinated voluntary movements begin to form in the 4^th month * Myelination of brain only begins in 9^th month * E.g. corticospinal tract myelination incomplete at birth, as evidenced by increasing infant mobility in the 1^st year

Question 40

**Sensory and motor system**

Answer 40

* No movement until 8^th week * At 8^th week- startle movement * Thereafter a large repertoire of movements develop * Practising for post-natal life e.g. suckling (sucking thumb), breathing

Question 41

* **‘quickening’**

Answer 41

* Maternal awareness of fetal movement’s from 17 weeks onwards * Felt earlier in subsequent pregnancy * Low cost, simple method of antepartum fetal surveillance * Reveal those foetuses requiring follow up

Question 42

cerebellar devlopment and corticospinal tracts being to form at

Answer 42

week 16

Question 43

myelination of spinal cord begins at

Answer 43

week 20

Question 44

charactersitic gyri and sulci appear as cerebellar hemispheres frow larger than the skull

Answer 44

week 28

Question 45

myelination begins in the brain

Answer 45

week 36