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MED6113 > Fetal Growth > Flashcards

Fetal Growth Flashcards

1
Q

What is intrauterine growth restriction?

A

fetus in unable to achieve its genetically predetermined size

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2
Q

How are small for gestational age foetuses classified?

A
  1. normal small foetuses
  2. abnormal small foetuses - have chromosomal or structural abnormalities
  3. growth restricted foetuses - as a result of placental dysfunction where the placenta is not providing enough nutrients
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3
Q

How is fetal growth restriction classified?

A
  • Symmetrical - fetal insult occurs in early development

* Asymmetrical - fetal brain is larger than the other parts of the body. fetal insult occurs in late development

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4
Q

What are some maternal risk factors of IUGR?

A
  • High altitudes –> maternal hypoxia
  • Drugs
  • CVS disorders
  • Chronic infections
  • Chronic renal disease
  • Antiphospholipid syndrome
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5
Q

What are some fetal risk factors of IUGR?

A
  • Multiple pregnancy
  • Infections of the fetus
  • Chromosomal abnormalities
  • Placenta or umbilical cord defects
  • Extrauterine pregnancy
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6
Q

What are the common chromosomal anomalies associated with IUGR?

A
  • Trisomy 21 - Down’s syndrome
  • Trisomy 13 - Patau’s syndrome
  • Trisomy 18 - Edward’s syndrome
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7
Q

When is fetal growth most vulnerable to maternal dietary deficiencies?

A

During embryo implantation and period of rapid placental development

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8
Q

How does maternal overnutrition or undernutrition affect fetal growth?

A
  1. Maternal undernutrition or overnutrition leads to reduced placental arginine and ornithine transport
  2. This leads to reduced placental + fetal arginine levels and reduced placental + fetal ornithine levels
  3. Reduced arginine results in reduced NOS activity, which leads to reduced NO levels
  4. This reduces placental angiogenesis and therefore reduces placental blood flow
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9
Q

What is the thrifty phenotype hypothesis?

A

A metabolically deprived developing foetus becomes metabolically programmed for insulin resistance and impaired glucose metabolism –> type II diabetes

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10
Q

How is the mother clinically assessed for fetal growth?

A
  • Symphysio-fundal height assessment - measures the upper border of the pubic symphysis to the upper border of the uterus. Smaller measurement = smaller baby.
  • Low sensitivity
  • High accuracy
  • Afterwards, use ultrasound to measure fetal biometry
  • Use ultrasound to measure amniotic fluid volume –> low volume indicates small baby
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11
Q

What would the uterine artery Doppler look like in cases of IUGR or preclampsia?

A

Poor placentation leads to high resistance in uterine artery, resulting in a Doppler with a:

  • Early diastolic notch
  • Reduced end-diastolic flow
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12
Q

When is an umbilical Doppler used?

A

To determine if a baby is at a high risk of mortality and morbidity.

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13
Q

What would the umbilical Doppler look like if the baby is at high risk of perinatal mortality and morbidity?

A

Extremely high resistance results in a Doppler with:

  • High peak systolic
  • Reversal in end-diastolic - negative flow of blood in the opposite direction
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14
Q

What is the middle cerebral artery Doppler used for?

A
  • Detects cerebral vasodilatation in small babies, which results in increased diastolic blood flow –> indicates that the baby needs to be monitored more closely
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15
Q

What would the ductus venosus Doppler look like if the baby is at risk of stillbirth?

A

In growth restricted babies, there is negative flow of blood during diastole
Use this to determine when to deliver the baby.

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16
Q

What are the important indicators for timing of delivery before 32 weeks?

A
  • abnormal ductus venosus pulsatility index

- reduced short term variability of fetal heart rate

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17
Q

What medication can be taken to prevent growth restriction?

A

Aspirin daily - reduces coagulability of blood, preventing growth restriction
- low MW heparin

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18
Q

How do you diagnose growth restriction in neonates.

A
  • low ponderal index
  • low subcutaneous fat
  • hypoglycemia
  • raised bilirubin levels
  • necrotising enterocolitis
  • high haemoglobin counts
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19
Q

What is macrosomia?

A

Birth weight of over 4000g regardless of gestational age

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20
Q

What is the greatest risk factor of macrosomia?

A

Maternal hyperglycaemia - high blood sugar during pregnancy

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21
Q

How does parity affect fetal growth?

A

The more pregnancies the mother has had, the bigger the baby will be because the uterus expands more quickly, giving the baby more chance to grow.

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22
Q

Describe fetal growth throughout gestation.

A

Fetal growth is slow until week 20.

Afterwards, fetal growth accelerates to reach a peak at weeks 30-36, then slows again.

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23
Q

When can the fetal heart beat be first detected?

A

6 weeks

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24
Q

What is the average birth weight?

A

3.5kg

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25
Q

Describe the role of the umbilical vein in the fetal circulation

A

The umbilical vein contains oxygenated blood from the placenta and enters the abdomen.
The umbilical vein divides into:
* A blood vessel supplying the liver
* Ductus venosus - enters the right atrium. Blood passes through the foramen ovale into the left side of the heart.

26
Q

What is the crista dividens?

A

Membranous valve in the right atrium preventing oxygenated blood from the ductus venosus and deoxygenated blood from the superior vena cava from mixing

27
Q

What are the 3 shunt systems that exist in the fetal circulation to maximise oxygen and nutrient transfer from the placenta to the developing organs?

A

Ductus venosus - shunts blood away from the liver to the right atrium
Foramen ovale - shunts blood from the right to left atrium
Ductus arteriosus - shunts blood from the pulmonary artery to the aorta

28
Q

Why does the ductus arteriosus remain patent prior to birth?

A

Prostaglandin E2 and prostacyclin production –> vasodilators

29
Q

How does the foramen ovale close?

A

At birth, umbilical vein blood flow stops, which stops blood flow in ductus venosus.
This results in fall in right atrium pressure and fall in pulmonary vascular system pressure so blood flows into the lungs rather than through the foramen ovale.

30
Q

How does the ductus arteriosus close?

A

Lung ventilation opens the pulmonary circulation, which causes a fall in pulmonary vascular resistance.

31
Q

Persistent fetal circulation

A

delayed closure of the ductus arteriosus because pulmonary vascular pressure does not fall. shunting of blood from aorta through the ductus arteriosus to the lung.
baby remains cyanosed and may suffer from hypoxia.
reduced blood flow to the GI tract and brain –> necrotizing enterocolitis and intraventricular haemorrhage.

32
Q

When does alveoli develop in the fetus?

A

24 weeks

33
Q

What is the role of surfactant?

A

Lines alveoli to prevent collapse during expiration by lowering surface tension

34
Q

What produces surfactant?

A

Type II pneumocytes

35
Q

When, in foetal development, does maximum surfactant production occur?

A

After 28 weeks

36
Q

Which hormone enhances the production of lecithin (predominant phospholipid in surfactant)

A

Cortisol

37
Q

What is the main reason why amniotic fluid may not be remaining in the amniotic cavity?

A

Preterm rupture of the membranes

38
Q

What is oligohydramnios?

A

Reduced amniotic fluid present in the amniotic cavity for the fetus to use for its lungs, resulting in reduced intrathoracic space. This may result in pulmonary hypoplasia, leading to progressive respiratory failure from birth.

39
Q

When should corticosteroids be administered antenatally to mothers at risk of preterm delivery?

A

24 hours before delivery.

40
Q

Describe the process of haemopoeisis in the fetus during gestation.

A

From 14-19 days after conception, RBCs are made from the yolk sac.
From 6 weeks, RBCs are produced by the liver
At 7-8 weeks, RBCs start to be made by the bone marrow and from 26 weeks gestation, the bone marrow is the predominant source of RBCs

41
Q

What is fetal haemoglobin composed of?

A

2 alpha and 2 gamma chains

42
Q

Describe the switch in haemoglobin during gestation.

A

From 10-28 weeks, HbF dominates
From 28 weeks to 34 weeks, a switch to HbA occurs
After birth, HbA dominates

43
Q

Thalassaemia

A

No or abnormal Hb production

44
Q

When do lymphocytes start to appear in the fetal immune system?

A

8 weeks

45
Q

What is detection of IgM and IgA in the newborn without IgG indicative of?

A

Fetal infection

46
Q

What are the general immunological defences in the fetus?

A
  • Amniotic fluid - contains lysosymes and IgG
  • Placenta - acts as a barrier against pathogens and contains phagocytes + lymphoid cells
  • Granulocytes from liver and bone marrow in circulation
  • Interferon from lymphocytes
47
Q

What does the skin of preterm babies look like?

A

No vernix and thin skin - allows proportionately large amount of insensible water loss from the skin.

48
Q

When does the midgut re-enter the abdominal cavity?

A

12th week

49
Q

Omphalocoele

A

Bowel and part of the liver contained in a sac due to failure of the midgut to re-enter the abdominal cavity.

50
Q

What is gastroschisis?

A

Bowel is separate and free-floating due to failure of the midgut to re-enter the abdominal cavity

51
Q

What is polyhydramnois?

A

Excess amniotic fluid in the amniotic cavity

52
Q

What can cause polyhydramnois?

A

Neurological abnormalities - baby lacks ability to swallow amniotic fluid
Obstruction of oesophagus

53
Q

Describe fetal liver development.

A

18th day of embryonic life - primitive liver appears as a diverticulum outpouching from the foregut

25th day - T shaped outgrowth invaded by blood vessels

Gives rise to parenchymal cells and hepatic ducts and other portion gives rise to gallbladder

54
Q

How does the fetal liver differ from the adult liver?

A

Reduced ability to conjugate bilirubin –> preterm babies are more prone to jaundice

55
Q

When is nephrogenesis complete?

A

36 weeks

56
Q

What is renal agenesis?

A

Condition where the kidneys do not form, resulting in severe oligohydramnios

57
Q

What is the fetus’ primary energy source?

A

Carbohydrate

58
Q

How may pregnancy result in gestational diabetes?

A

During early pregnancy, progesterone makes tissues less sensitive to insulin so maternal tissues absorb less glucose, resulting in higher glucose availability for the fetus.

59
Q

Why do the mother’s bones become thinner during pregnancy?

A

Maternal bones are being demineralised to provide calcium for the baby –> helps bone formation of fetus

60
Q

What is the role of 2,3-DPG?

A

Reduces oxygen binding

MED6113 (9 decks)

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