L5 Normal and Disordered Foetal Growth

Question 1

How are small-for-GA babies classified?

Answer 1

• Normal small fetuses: no structural abnormality, normal umbilical artery Doppler and liquor -> Not at risk, no special care needed
• Abnormal small fetuses: chromosomal/structural abnormalities -> specialised care and counselling
• Growth restricted fetuses: placental dysfunction, necessitating treatment and careful timing of delivery

Question 2

Define ‘small for gestational age’:

Answer 2

• Fetus is within 10th weight percentile for its age (in weeks)

Question 3

Define intrauterine growth restriction:

Answer 3

• Fetus is unable to achieve its genetically predetermined size

Question 4

What qualifies as low birth weight?

Answer 4

• Less than 2500gms
• Baby could be SGA or could simply pre born prematurely

Question 5

What percentage of SGA babies are considered normal vs ‘at-risk’?

Answer 5

• 40% healthy, 40% growth restricted
• Those that are actually healthy should not be subjected to risky protocols or risk iatrogenic prematurity
• Only the growth-restricted fetuses are at risk of potentially preventable perinatal death

Question 6

How is FGR classified and what contributes to each?

Answer 6

• Symmetrical or asymmetrical
• Related to underlying cause of growth delay and the duration of the insult

Question 7

Describe symmetrical FGR:

Answer 7

• Fetal head and body are proportionately small
• Fetal insult occurring during early development, impacting growth processes and cell hyperplasia

Question 8

Describe asymmetrical FGR:

Answer 8

• Fetal brain disproportionately large compared to liver (ratio >6)
• Fetal insult during later development -> distinct growth patterns by differential impacts on axial and peripheral skeletal growth
• Potential link to brain sparing effect

Question 9

What is the brain sparing effect?

Answer 9

• Blood flow prioritised to brain over other areas during development
• Response to placental insufficiency

Question 10

What groups of risk factors exist for FGR?

Answer 10

• Maternal (age, height, genetics, other conditions, lifestyle etc)
• Placental and cord abnormality
• Fetal factors (often congenital)
• Infections (TORCH, malaria)

Question 11

What lifestyle factors can increase risk of fetal growth restriction? (x3)

Answer 11

• Drug use/abuse: marijuana, opiates, cocaine, smoking, drinking, chemotherapy, and others
• Under/overnutrition
• Altitude

Question 12

List some placental and cord abnormalities:

Answer 12

• Incorrect cord insertion
• Single umbilical artery
• Placental tumour
• Circumvillate placenta
• Defective trophoblastic invasion/placentation
• Reduced blood flow to placental bed e.g. preeclampsia
• Vascular anomalies e.g. TTTS
• Decreased functioning mass: Small placenta, abruption, placenta praevia, post term pregnancy

Question 13

Give examples of infections that are risk factors for FGR:

Answer 13

• TORCH
• TB
• Malaria -> can invade placenta and damage its function
• Parvo virus B19

Question 14

What is the underlying mechanism of IUGR?

Answer 14

• Insufficient gas exchange and nutrient delivery to fetus
• Often as a result of reduced capacity to carry/deliver/recieve oygen

Question 15

What factors can cause placental damage?

Answer 15

• Smoking
• Thrombophilia
• Autoimmune diseases

Question 16

What factors can reduce oxygen carrying capacity of the mother?

Answer 16

• Cyanotic heart disease
• Smoking
• Haemoglobinopathy

Question 17

What factors can impair oxygen delivery to the fetus:

Answer 17

• Diabetes with vascular disease
• Hypertension
• Autoimmune conditions

Question 18

Outline the thrifty phenotype hypothesis:

Answer 18

• Nutritional insult during critical period of gestation may permanently impact the child
• Maternal nutritional status can alter epigenetic state of fetal genome and imprint gene expression
• Examples include development of T2DM, metabolic syndromes

Question 19

Why is timing so important in delivery of FGR babies?

Answer 19

• Increased fetal morbidity and mortality -> 10x increase in late fetal deaths among very small fetuses

Question 20

List some perinatal implications of FGR:

Answer 20

• Stillbirth (40% non-malformed stillbirths are SGA)
• Prematurity -> nacrotizing enterocolitis, ischaemic bowel, thrombocytopenia, temperature instability, renal failure, metabolic problems
• Asphyxia
• Congenital malformations

Question 21

Long-term consequences of FGR: (mother)

Answer 21

• Abnormalities of hypothalamic pituitary axis
• Cardiovascular disease
• Insulin resistance
• Metabolic syndrome

Question 22

Long term consequences for FGR children:

Answer 22

• LBW associated with high cholesterol
• Associated with decresed stroke volume, abnormally globular ventricles, high BP, increased intima-media thickness
• Other: Poor physical and intellectual performance by various metrics, behavioural problems

Question 23

How can aspirin improve outcomes of IUGR?

Answer 23

• Prevents aggregation of platelets
• Thinning of blood improves flow
• Particularly useful in cases of preeclampsia

Question 24

Evidence for clinical examination of IUGR using symphysio-fundal height:

Answer 24

• Poor sensitivity and specificity, not particularly fallible
• Benefits from being cheap and quick, can be conducted by the midwife
• Predictive value can possibly be improved using customisation of charts (age, ethnicity, weight and parity) -> improved sensitivity to detect SGA

Question 25

What aspects of fetal biometry might be measured to help diagnose SGA?

Answer 25

* Biparietal diameter * Head circumference * Abdominal circumference * Femur length * Estimated fetal weight * Amniotic fluid volumes (via deepest vertical pocket)

Question 26

What surveillance is typically carried out for mothers at risk of FGR?

Answer 26

* Serial scans * Antenatal cardiocography (CTG) * Amniotic fluid volume assessment * Umbilical doppler * Biophysical profile assessment

Question 27

What test is done on FGR neonates?

Answer 27

* Ponderal index (relationship between height and weight) -> Low? * If low, can indicate hypoglycaemia, hyperbilirubinemia, necrotising enterocolitis, hyperviscosity syndromes

Question 28

How may FGR be prevented?

Answer 28

* Known to be largely unpreventabe * Some evidence of benefit for... * LDA and miniheparin * Reducing smoking * Antibiotics to prevent UTIs * Antimalarial prophyaxis

Question 29

What is the key idea in fetal surveillance in cases of FGR:

Answer 29

* Careful monitoring to time delivery * Waiting until risk of in utero demise outweighs risk of delivery and prematurity

Question 30

Define fetal macrosomia and LGA:

Answer 30

* LGA: Above 90th percentile * Macrosomia: BW>4000g regardless of GA

Question 31

How common is macrosomia?

Answer 31

* 9 - 10% neonates * Geographical variation -> potential genetic and envirnomnental factors

Question 32

List the key risk factors associated with macrosomia:

Answer 32

* Obesity * Diabetes (GDM/T2DM) * Postterm gestation * Multiparity * Stature of parents * Advanced maternal age * Previous macrosomic infant * Ethicity

Question 33

What are the key complications associated with fetal overgrowth?

Answer 33

* Maternal diabetes * Fetal demise * Birth trauma -> shoulder dystocia, nerve palsies * Neonatal hypoglycaemia

Question 34

What is the **greatest** risk factor for macrosomia?

Answer 34

* Maternal hyperglycaemia * Accelerates fetal growth * Alters body proportions