Fetal Growth and Development Flashcards

1
Q

What is the fetal period?

A

Growth and physiological maturation of the structures created during the (very much shorter) embryonic period.

Period involving preparation for the transition to independent life after birth

Weeks 9 to 38

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2
Q

In terms of growth and activity how do the embryonic and fetal period compare?

A

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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3
Q

Describe the differential growth of a fetus (from pre-embryonic).

A

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

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4
Q

How do body proportions change during fetal period?

A

Dramatically
- At 9 week, the head is approx. half CRL
- Thereafter, body length & lower limb growth
accelerates

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5
Q

What are the ante-natal assessments of fetal well-being?

A
Mother
- Fetal movements
Regular measurements of uterine expansion
- Symphysis-fundal height
Ultrasound scan
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6
Q

Tell me about the obstetric ultrasound scan (USS)

A

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

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7
Q

How do you estimate fetal age?

A
From last menstrual period (LMP)
- Prone to inaccuracy
Developmental criteria
- Allow accurate estimation of fetal age
- Crown-rump length (CRL)
- Biparietal diameter
- Abdominal circumference & femur length
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8
Q

Tell me about crown-rump length.

A

Measured between 7 & 13 weeks to date the pregnancy and estimate EDD (estimated date of delivery)
Scan in T1 also used to check location, number, viability

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9
Q

Tell me about biparietal diameter.

A

The distance between the parietal bones of the fetal skull

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

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10
Q

Tell me about abdominal circumference & femur length.

A

AC & FL used in combination with BPD for dating and growth monitoring
Also useful for anomaly detection

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11
Q

Tell me about 3-D or 4-D USS.

A

New wave of obstetric ultrasonography
Not likely to replace standard USS
- Complimentary tool

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12
Q

What are the different classifications of birth-weights?

A

3500g is considered average
4500g is macrosomia
- Maternal diabetes
Many factors influence birth weight, not all pathological

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13
Q

What is the importance of accurate dating?

A

Babies can have low birth-weight because

  • They are premature OR
  • They are constitutionally small OR
  • They have suffered growth restriction
    • Associated with neonatal morbidity & morality
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14
Q

Describe the development of the respiratory system in the fetus.

A

The lungs develop relatively late
- Embryonic development creates only the
bronchopulmonary tree
- Functional specialisation occurs in the fetal period
- Major implication for pre-term survival

Weeks 8-16: pseudoglandular stage
- Duct system begins to form within the 
  bronchopulmonary segments created during the 
  embryonic period
     - Bronchioles

Weeks 16-26: canalicular stage
- Formation of respiratory bronchioles
- Budding from bronchioles formed during the
pseudoglandular stage

Weeks 26 - term: terminal sac stage
- Terminal sacs begin to bud from the respiratory 
  bronchioles
- Differentiation of:
     - Type I & Type II pneumocytes
           - Surfactant
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15
Q

Describe the lungs of the fetus during T2 & T3 of pregnancy.

A

Gas exchange conducted at placenta, but lungs must be prepared to assume full burden at birth
“Breathing” movements
- Conditioning of the respiratory musculature
Fluid filled
- Crucial for normal lung development

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16
Q

How are the lungs related to implications for pre-term survival?

A

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

17
Q

Explain respiratory distress syndrome.

A

Often affects infants born pre-maturely
Insufficient surfactant production
If pre-term delivery is unavoidable or inevitable
- Glucocorticoid treatment (of the mother)
- Increases surfactant production in fetus

18
Q

Tell me a little bit about the development of the fetal cardiovascular system.

A

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

19
Q

Tell me a little bit about the development of the fetal urinary system.

A

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, but without it there is oligohydramnios

20
Q

What is the importance of amniotic fluid volume?

A

Oligohydramnios
- Too little
- Placental insufficiency, fetal renal impairment
Polyhydramnios
- Too much
- Fetal abnormality - e.g. inability to swallow

21
Q

Tell me a little bit about the development of the fetal nervous system.

A

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

22
Q

Tell me a little about the movement of fetus’.

A

No movement until the 8th week

Thereafter a large repertoire of movements develop

  • “Practising” for post-natal life
    • e.g. suckling, breathing
23
Q

What are the implications of fetal movements?

A

“Quickening”
- When there is maternal awareness of fetal movements
from 17 weeks onwards
- Low cost, simple method of ante-partum fetal
surveillance
- Reveal those fetuses requiring follow-up