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REPRO > Lecture 17: Fetal development > Flashcards

Lecture 17: Fetal development Flashcards

1
Q

What happens during the fetal period?

A

Growth and physiological maturation of the structures created in the embryonic period

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2
Q

What are the different stages from fertilisation to birth?

A
  • pre-embryonic (1-2 weeks)
  • embryonic (3-8 weeks, where risks of congenital structural defects is highest)
  • fetal (9-38 weeks, brain is only structure susceptible to damage here as it is still developing)
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3
Q

When are pregnancy weeks counted from?

A

First day of the last menstrual period

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4
Q

What is the pattern of growth in the embryonic period?

A

-intense activity
-organogenetic period
-absolute growth is very small (except placental growth)
(we see growth and weight gain accelerate in the fetal period)

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5
Q

What is a good measurement of size in the early stages of pregnancy?

A

Crown rump length (CRL)

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

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6
Q

What causes weight gain in the fetus?

A

Embryo: intense morphogenesis and differentiation, little weight gain, placental growth most significant
Early fetus: protein deposition
Late fetus: adipose deposition (particularly brown adipose)

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7
Q

What is the CRL at 38 weeks?

A

36 cm

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8
Q

How does the fetus’ body proportions change throughout the pregnancy?

A

9 weeks: head is half the CRL
Fetal period: body length and lower limb growth accelerates
(even at birth the head is a quarter of the CRL)

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9
Q

How do we do an ante-natal assessment of fetal wellbeing?

A
  • fetal movements (seen in 2nd trimester)
  • regular measurements of uterine expansion (symphysis-fundal height)
  • USS (safe)
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10
Q

What is the purpose of an obstetric USS?

A

-can be used in early pregnancy to calculate age
-rule out ectopics
-number of fetuses
(routinely carried out at 20 weeks: assess fetal growth and see fetal abnormalities as structures are big enough)

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11
Q

How do we estimate fetal age?

A
  • LMP: prone to inaccuracy

- developmental criteria e.g. size/growth curves (allows accurate estimation of fetal age)

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12
Q

What is the crown rump length?

A

From top of head to bottom of torso
-measured b/w 7-13 weeks to date the pregnancy and estimate the EDD
(good as little biological variance at this stage)

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13
Q

What is the biparietal diameter?

A

Distance between the parietal bones of the fetal skull

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14
Q

What is used for dating and monitoring growth after 13 weeks?

A

-biparietal diameter
-abdominal circumference
-femur length
(usually done at 20 week scan)

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15
Q

What is 4D USS?

A

New wave of obstetric ultrasonography

  • not currently replacing standard USS, used as a complimentary tool
  • really good at detecting congenital abnormailities
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16
Q

How do you classify birth weights?

A

3500g is average
<2500g suggests growth restriction
>4500g is macrosomia (maternal diabetes)
(many factors influence birth weight, not all pathological)

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17
Q

Why can babies have a low birth weight?

A
  • premature (low birth weight is not abnormal here)
  • constitutionally small (small mother)
  • suffered growth restriction (associated with neonatal morbidity and mortality): ante-natal screening used to pick up on this group
18
Q

What are the last structures to develop?

A

Lungs/respiratory system

  • embryonic development creates only the bronchopulmonary tree
  • functional specialisation occurs in the fetal period
19
Q

Where do the lungs develop from in the embryonic period?

A
  • respiratory diverticulum is the outpouching of the primitive gut tube (endoderm)
  • tracheoesophageal septum separates the respiratory and GI tracts
  • respiratory diverticulum grows into the trachea and bronchi branch off (only make airways during the embryonic period)
20
Q

What is the stages of lung development in the fetal period?

A

Pseudoglandular stage: duct system begins to form within the bronchopulmonary segments created during the embryonic period, forming bronchioles
Canalicular stage: formation of respiratory bronchioles
Terminal sac stage: terminal sacs begin to bud from the respiratory bronchioles, differentiation of type 1 and 2 pneumocytes to develop the alveolar membrane- allow for surfactant production

21
Q

How are the lungs prepared to assume full burden of gas exchange at birth?

A

Gas exchange is conducted at the placenta but lungs need to be ready at birth

  • ‘breathing’ movements: allow for conditioning of the respiratory musculature
  • lungs are fluid filled with amniotic fluid: crucial for normal lung development
22
Q

What is the threshold of viability?

A

Fetal viability cannot be continually pushed back as there is a limit beyond whichthe lungs will not be sufficiently developed to sustain life
-viability is only a possibilty once the lungs have entered the terminal sac stage of development e.g. 24 weeks

23
Q

What is respiratory distress syndrome?

A

-often affects infants born prematurely
-insufficient surfactant production
If pre-term delivery is unavoidable/inevitable:
-glucocorticoid treatment of mother, this increases surfactant production in the fetus

24
Q

When is the definitive fetal heart rate achieved by?

A

15 weeks

25
Q

When does fetal kidney function begin?

A

10 weeks

26
Q

Without fetal kidney function what occurs?

A

Oligohydramnios

although fetal kidney function is not necessary for survival in utero

27
Q

What causes oligohydramnios?

A
  • fetal renal impairment

- placental insufficiency

28
Q

What is polyhydramnios?

A

Too much amniotic fluid

-fetal abnormality e.g. inability to swallow

29
Q

What system is the first to begin development and last to finish?

A

Nervous system

  • from neural tube
  • corticospinal tracts which are required for coordinated voluntary movements begin to form in the 4th month of pregnancy
  • myelination of brain only begins in the 9th month of pregnancy (see evidence of this from increasing infant mobility in the first year)
30
Q

When does movement of the fetus begin?

A

8th week

-after this there is a large repetoire of movements e.g. practicing for post-natal life (suckling, breathing)

31
Q

What is ‘quickening’?

A

Maternal awareness of fetal movements from 17 weeks onwards

-low cost, simple method of ante-partum fetal surveillance

32
Q

What is the etiology of fetal heart rate accelerations in utero?

A

Response to fetal movement

33
Q

What is normal fetal pO2?

A

4 kPa

34
Q

What is the normal fetal heart rate?

A

110-160 bpm

35
Q

Which prenatal diagnostic test has the highest risk of pregnancy loss?

A

Chorionic villus sampling

36
Q

What is the most common fundal height at 36 weeks?

A

Xiphisternum (lowest part of the sternum)

37
Q

What is the most common fundal height at 20 weeks?

A

Umbilicus

38
Q

What is the most common fundal height at 16 weeks?

A

Mid-way between pubis and umbilicus

39
Q

What is the most common fundal height at 12 weeks?

A

Pubic symphysis

40
Q

What supplementation should women take in pregnancy to help promote healthy development of the fetal nervous system?

A

Folic acid to prevent neural tube defects e.g. spina bifida

REPRO (18 decks)

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