4. Fetal Growth

Question 1

What are the two things responsible for the extent of fetal growth?

Answer 1

○ Genetic potential- derived from both parents, and reflects the logical view that taller/ bigger parents will have infants that are different in size to parents who are shorter or lighter in build. Mediated by factors under genetic control.
○ Substrate supply - sufficient nutrients are essential to achieve genetic potential. Primarily based on placenta.

Question 2

What are the different stages of fetal growth and the times that they occur in?

Answer 2

○ Cellular hyperplasia (4-20 weeks of gestation) - rapid cell division and multiplication where the cell grows into a foetus
○ Hyperplasia and hypertrophy (20-28 weeks) - cells increase in size
○ Domination of hypertrophy (28-40 weeks) - rapid increase in cell size and accumulation of muscle, fat and connective tissue

Question 3

How does weight gain change throughout pregnancy?

Answer 3

○ 14-15 weeks – 5g/day
○ 20 weeks - 10g/day
○ 32-34 weeks – 30-35 g/day
After 34 weeks growth rate decreases

Question 4

How can the size of the infant be determined?

Answer 4

Determination of the Symphysis Fundal Height (SFH) - the symphysis fundal height is measured
Take a tape measure and measure the height of the fundus to the symphysis pubis. Each cm roughly equals to the number of weeks of pregnancy
Palpitation of the maternal abdomen can also be used
Changes in SFH with gestational age reflects generic changes in uterine size but it is vulnerable to a variety of errors

Question 5

What would lower or higher values of weight than expected suggest?

Answer 5

Lower values - Wrong last menstrual period date, baby in a transverse lie, or complications such as oligohydramnios (deficiency of amniotic fluid)
Higher values - wrong last menstrual period, multiple pregnancy, or maternal obesity.

Question 6

What are the pros and cons of measuring symhysis fundal height to determine fetal growth?

Answer 6

Pros: simple and inexpensive
Cons: influenced by many factors such as BMI etc, results vary on who interprets it and there is also a low detection in any complications

Question 7

Why is accurate dating of the pregnancy needed?

Answer 7

○ You don’t get confused if a baby is small or large (small for gestational age or large for gestational age)
○ So the correct decisions can be made on how the baby should be delivered
○ Steroids can be given if needed

Question 8

How can pregnancies be dated?

Answer 8

• All pregnancies are measured using the CRL (crown-rump length) apart from IVF pregnancies where the embryo transfer date is used
• After 14 weeks or when the baby is larger than 84 cm, the pregnancy can be dated using head circumference

Question 9

What are the four biometrical parameters used to assess fetal growth using ultrasound?

Answer 9

○ Parietal diameter (BPD)
○ Head circumference (HC)
○ Abdominal circumference (AC)
○ Femur length (FL).

Question 10

What are the biometrical parameters used to do?

Answer 10

They are combined to give the estimated fetal weight (EFW). Normative growth curves have been constructed from these ultrasound measurements (expressed in centiles). Used clinically to identify a normal intrauterine growth and detect risk of obstetric and neonatal complications.

Question 11

Why is ultrasound needed?

Answer 11

• Assessment of fetal wellness not just size – how is the baby moving, how is the amniotic fluid
• Looking at trends in growth
• Predict fetal compromises that may occur
• Anticipate if a premature delivery is needed
• To provide the right arrangements for the baby after it is born

Question 12

What are the different factors that influence fetal growth?

Answer 12

Maternal factors
Feto-placental factors
Hormones

Question 13

Give examples of maternal factors that influence fetal growth

Answer 13

Maternal factors influencing fetal growth include poverty, mother’s age, drug use, alcohol, smoking, diseases etc.

Question 14

How do feto-placental factors affect fetal growth?

Answer 14

Males are generally bigger than females; second and subsequent infancy pregnancies are generally heavier.

Question 15

How do hormones affect fetal growth?

Answer 15

Hormones have a role in regulating fetal growth, e.g. cortisol, thyroxine (for maturation of CNS esp in the 3rd trimester), pituitary growth hormone.
These fetal hormones promote growth and development in utero by altering both the metabolism and gene expression of the fetal tissues.
They ensure that fetal growth rate is proportional to the nutrient supply and that prepartum maturation occurs in preparation for extra-uterine life.

Question 16

What are customised fetal growth charts and why are they used?

Answer 16

These are based on fetal weight curves for normal pregnancies and adjusted to reflect maternal variation. They are optimised by presenting a standard free from pathological factors such as diabetes and smoking.
They can therefore be more specific towards a particular ethnicity or population – the current size of the baby can be compared to what it is predicted to be based off the mother rather than just comparing the baby to others

Question 17

What are two key terms/definitions for a variance in fetal weight?

Answer 17

SGA = small for gestational age
FGR = fetal growth restriction/ same thing as IUGR (Intra-uterine growth restriction )

Question 18

What is Intra-uterine growth restriction (IUGR)?

Answer 18

IUGR= failure of infant to achieve its predetermined (genetic) potential for a variety of reasons.

Question 19

When does IUGR generally develop

Answer 19

In the second and third trimesters of pregnancy- almost all weight gain occurs in the later stages of pregnancy

Question 20

What are the factors that can reduce fetal growth and cause IUGR?

Answer 20

○ Maternal medical factors- chronic hypertension, connective tissue disease, severe chronic infection
○ Maternal behavioral factors- smoking, poor nutrition, age <16 or >35
○ Fetal factors- multiple pregnancy, structural abnormality, chromosomal abnormality
○ Placental factors- impaired trophoblast invasion, partial abruption/ infarction, chorioamnionitis.

Question 21

What is the link between pre-eclampsia and fetal growth?

Answer 21

Close link between pre-eclampsia and IUGR as the main cause of pre-eclampsia is diminished remodeling of the spiral arteries which causes decreased blood flow and hence a decreased nutrient supply to placenta and fetus.

Question 22

What is the treatment for pre-eclampsia/ IUGR?

Answer 22

Difficult to treat IUGR or pre-eclampsia once they have been identified. Corticosteroids should be administered at gestation to improve neonatal wellbeing, especially lung development. Ultimate treatment for pre-eclampsia is delivery as the placenta is the primary cause; emergency caesarean section may be necessary.

Question 23

What is pre-eclampsia?

Answer 23

• Defined as hypertension in the mother (BP is greater than 140/90) and significant proteinuria (more than 0.3g/hour)
• This will also cause oedema

Question 24

When does pre-eclampsia occur?

Answer 24

It usually arises after 20 weeks in the second trimester and resolves completely 6 weeks post-partum

Question 25

What does a low birth weight usually lead to?

Answer 25

Pre-term delivery

Just because the baby has a low birth weight does not mean they are growth restricted

Question 26

What is fetal growth restriction and how can the growth of the fetus be assessed?

Answer 26

The baby has to have had a change in the growth velocity in order for the term fetal growth restriction to be used
Fetal biometry should be measured every 10 days and not every day so that you can see how they are growing

Question 27

What are the short, medium and long term consequences of FGR/LBW?

Answer 27

Short term:
Respiratory distress (minimised by giving steroids to the mother)
Sepsis, Intraventricular haemorrhage, Hypoglycaemia, Jaundice

Medium term:
Respirotory problems, developmental delay
The more premature the baby is born, the higher the risk of any conditions in the medium term

Long term:
Fetal programming
There is an increased risk of IUGR and intrauterine death in the mother’s next pregnancy

Question 28

What are the causes of being small for gestational age (SGA)?

Answer 28

• Dating problem – if this is suspected then the mother is told to come back in after 2 weeks to monitor for a consistent growth and to check if they are growing along the same centile
• Fetal problem – this is much more serious. If the fetus is very small from the beginning then you need to think if it is an underlying chromosomal abnormality or a congenital fetal infection (e.g. toxoplasmosis)
• Placental insufficiency – this is brain sparing so there will be a reduction in growth of the abdominal circumference first with a normal head circumference. Then over time there will be a reduction in the amniotic fluid

Question 29

What is placentation?

Answer 29

Placentation - the formation or arrangement of a placenta in a woman’s uterus
Occurs in weeks 10-12

Question 30

Outline how a blood supply to the placenta formed? How is this different in woman with pre-eclampsia?

Answer 30

• A non-pregnant uterus would have spiral arches
• When you are pregnant, the arches undergo trophoblastic invasion so become much wider and can accommodate an increased blood flow in the placenta
• This process doesn’t happen in woman who have pre-eclampsia or fetal growth restriction and the vessels remain very narrow. This causes a high shear force of the blood and an increased resistance in the placenta

Question 31

Which fetuses need growth monitoring

Answer 31

Bad obstetric history - previous maternal HTN, previous FGR or stillbirth
Concerns with current pregnancy - reduced symphysis fundal height, maternal systemic disease (HTN, renal coagulation), antepartum haemorrhage, abnormal serum biochemistry

Question 32

What is a uterine artery doppler?

Answer 32

• Used in the 1st or 2nd trimester to screen for woman at risk
• It will check for the resistance in the vessels so if pressure is too high, the possible hypertension in the mother can be identified and the pregnancy can be monitored more closely
• Used to screen for pre-eclamptic toxaemia (PET) - a woman with an abnormal reading is 5 times more likely to have PET and 3.5 times more likely to have fetal growth restriction

Question 33

What generally happens to the baby as it becomes hypoxic?

Answer 33

• As the baby becomes more hypoxic, it will divert the blood to the brain, heart and adrenals
• There will be many changes that take place, ultimately leading to changes in the fetal breathing and HR patterns

Question 34

How does blood flow and blood vessel structure change in a hypoxic baby?

Answer 34

• The circle of Willis is where the middle cerebral artery is found and as the baby becomes more hypoxic, there will be a reduced resistance to blood flow so that more blood can flow to the head
• The ductus venosus shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. As the baby becomes more hypoxic, there will be changes to it as it has 40% of the venous umbilical blood flow
○ An abnormal ductus venosus is a very late change and the baby will need to be delivered within 24 hrs

Question 35

Why is fetal movement counting important? How is this measured?

Answer 35

A reduction in fetal movements can precede fetal death by a day or more
Cardiff kick chart - record the time taken each day to count 10 fetal movements
Cardiac or ultrasound assessment is needed if there is a reduced movement

Question 36

How does delivery in pregnancies that are complicated by FGR differ?

Answer 36

Balance the risks to the mother and the baby

Steroids are usually given as they give the baby’s lungs a better chance of survival

Question 37

What does the mode of delivery depend on?

Answer 37

Condition of the pregnancy
State of the cervix
Presentation of the fetus
Other features (e.g. oligohydramnious - they have less fluid there will be cord compression during contractions so labour won’t be well tolerated

Question 38

When can an induction of labour be offered?

Answer 38

Over 36 weeks

Question 39

What are the differences between early and late IUGR?

Answer 39

Early IUGR:
Low incidence
Correlated with maternal diseases e.g. pre-eclampsia
Difficult to manage - balancing risk of being premature to in utero death

Late IUGR:
More common
Rarely related to pre-eclampsia
Difficult to differentiate between this and small for gestational age 
Easy to manage - deliver the baby