Fetal growth

Question 1

How can pregnancies be dated clinically?

Answer 1

1. Date of last menstruation (about 14 days before fertilisation)
2. Bi-parietal diameter measurement using ultrasound (~8-12 weeks)

Question 2

What are the simple tests (no equipment required) for measuring fetal growth?

Answer 2

1. Maternal weight gain
2. Uterine fundal height

Question 3

What are the measurments that can be taken with ultrasound to measure fetal growth?

Answer 3

1. Biparietal diameter
2. Head circumference
3. Crown (top of head)/rump (buttocks) length
4. Femur length
5. Abdominal diameter

Question 4

What are the definitions for abnormal fetal growth with regards to centile charts?

Answer 4

1. Small for gestational age (SGA): Below 10^th centile (indicates IUGR)
2. Large for gestational age (LGA): Above 90^th centile (indicates possibility for birth obstruction)

Question 5

What are the types of IUGR?

Answer 5

1. Symmetrical
2. Asymmetrical

Question 6

What is symmetrical IUGR?

Answer 6

The parts of the fetal body are all in proportion with each other, but the overall size is smaller than for gestational age. This usually indicates growth restriction beginning in the first trimester.

Question 7

What are the causes of symmetrical IUGR?

Answer 7

1. Intrauterine infections (e.g. toxoplasmosis)
2. Aneuploidy (and other chromosomal defects)
3. Maternal abuse of alcohol (fetal alcohol syndrome)

Question 8

What is asymmetrical IUGR?

Answer 8

The head of the fetus is much larger than its body. This usually indicates growth restriction sometime in the third trimester, resulting in diversion of nutrients away from the periphery in order to sustain growth of CNS.

Question 9

What are the causes of asymmetrical IUGR?

Answer 9

1. Pre-eclampsia
2. Malnutrition
3. Placental insufficiencies
4. Anaemia
5. Hypertension

Question 10

Which type of IUGR is most common?

Answer 10

Asymmetrical (3/4 of cases)

Question 11

What are the maternal factors that affect fetal growth?

Answer 11

1. Uterine size
2. Altitude
3. Nutrition
4. Parity
5. Socio-economic status
6. Disease
7. Stress

Question 12

How does uterine size affect growth?

Answer 12

The smaller the uterine size, the smaller the fetus tends to be as a consequence of spatial restriction.

Question 13

How does maternal nutrition affect growth?

Answer 13

Maternal malnutrition has different effects on fetal growth depending on stage of pregnancy (as was evident from Dutch hunger winter).

Question 14

What effects on fetal growth did the Dutch hunger winter have for women at different stages of pregnancy?

Answer 14

• If malnutrition in mother occurs in first trimester, but is restored thereafter, there is no decline in birth weight, but adult morbidity is increased.
• If malnutrition in mother occurs in third trimester, but is restored thereafter, there is decline in birth weight, but risk of adult morbidity is unaffected.

Question 15

How does altitude affect fetal growth?

Answer 15

• Maternal O₂ exposure (and thus O₂ available to fetus) is severely reduced at higher altitudes, which reduces birth weight.
• Average birth weight falls ~100g per 1000m above sea level.

Question 16

How does parity affect fetal growth?

Answer 16

First baby tends to smaller than second baby because the uterus and maternal physiology becomes more adapted to pregnancy after first pregnancy, so subsequent pregnancies are more ‘efficient’.

Question 17

How does maternal socio-economic status affect fetal growth?

Answer 17

• Low socio-economic status is correlated with low birth weight.
• Several possible explanations for this phenomenon:
  1. Early (teenage) pregnancy: Small uterine size
  2. Malnutrition
  3. Smoking/drug abuse

Question 18

How does maternal disease affect fetal growth?

Answer 18

Maternal diseases such as hypertension and cardiac insufficiency can affect her ability to supply fetus with adequate nutrition, thus cause fetal growth restriction.

Question 19

How does maternal stress affect fetal growth?

Answer 19

Increased levels of cortisol in maternal circulation may cause premature birth.

Question 20

What are the placental factors that affect fetal growth?

Answer 20

1. Blood flow
2. Infarction
3. Transporter expression
4. Barrier function

Question 21

How does placental blood flow affect fetal growth?

Answer 21

1. Failure for spiral arteries to remodel properly during placentation causes increased resistance in placental circulation.
2. This reduces blood supply to fetus and predisposes to condition such as IUGR in fetus but also pre-eclampsia in mother.

Question 22

How does placental infarction affect fetal growth?

Answer 22

Ischaemia of the placenta and subsequent tissue damage can reduce the surface area of feto-maternal exchange interface and thus cause growth restriction.

Question 23

How does placental transporter expression affect fetal growth?

Answer 23

In response to placental stress (e.g. reduced oxygenation), there may be reduced expression of many of the specialist transporters required for adequate nutrient exchange between mother and fetus (e.g. for glucose and amino acids), thus causing fetal growth restriction.

Question 24

How does placental barrier function affect fetal growth?

Answer 24

Disruption of barrier may result in maternal hormones and other factors (e.g. cortisol) leaking into fetal circulation and causing abnormal growth.

Question 25

What are the fetal factors that affect fetal growth?

Answer 25

1. Sex 2. Genome 3. Infection 4. Endocrine

Question 26

How does fetal sex affect fetal growth?

Answer 26

As a general trend, males on average have greater dimensions compared to females, including: 1. Birth weight 2. Length 3. Head circumference

Question 27

How does fetal genome affect fetal growth?

Answer 27

Fetal genetic abnormalities (e.g. aneuploidies) account for substantial proportion of IUGRs.

Question 28

How does fetal infection affect fetal growth?

Answer 28

Infections (e.g. rubella, HCMV, toxoplasmosis) also cause symmetrical IUGR.

Question 29

How does fetal endocrine factors affect fetal growth?

Answer 29

- The most important endocrine regulators of fetal growth are probably IGFs. - Defects in IGF expression lead to growth abnormalities.

Question 30

What are the symptoms of Beckwith-Wiedemann syndrome?

Answer 30

1. Macroglossia (large tongue) 2. Macrosomia (large birth size) 3. Organomegaly (enlargement of organs) 4. Anterior abdominal wall defects 5. Predisposition to childhood tumours

Question 31

What are the causes of BWS?

Answer 31

Over-expression of IGFII gene on chromosome 11 as result of epigenetic factors, including: 1. Paternal uniparental disomy 2. Abnormal imprinting resulting in activation of maternally imprinted IGF-II (normally deactivated).