Lecture 14: Very big and Very small Babies

Question 1

What are the poor health associations of low birthweight <2500g

Answer 1

• 6 x perinatal mortality and morbidity
• average drop of IQ 8 points
• increased inattention, hyperactivity, behavioural problems
• decreased post natal growth so 20% are short stature, associated with lower income
• increased adult non-communicable diseases eg. increased CVD, BP, Insulin resistance

Question 2

What are the poor health associations of high birthweight >4500 g and what maternal conditions contribute to this

Answer 2

Increased morbidity for Mother and baby

• Birth trauma - PPH, C section, genital tract injuries, birth injury
• high likelihood for neonatal hyperbilirubinaemia and hypoglycaemia as pancreas has to slow down after birth
• childhood obesity, adult non communicable disease - metabolic syndrome/diabetes, large babies and metabolic disease in the next generation
• Maternal obesity and gestational diabetes are key risk factors

Question 3

What are the 3 determinants of fetal growth in order of importance.
What is the effect of interaction with the nutritional environment

(Maternal constraint also one)

Answer 3

1. Substrate supply by the placenta: Nutrition availability
2. Fetal hormones for growth
3. Genetic growth potential (minimal effect)

This happens because the signals in utero about the environment - low or high nutrition cause epigenetic changes which create a phenotype best suited, but there is a mismatch leading to cvd in big babies and metabolic disorders like diabetes in small babies

Question 4

What is the main substrate for fetus which is actively managed and when can fetus get growth problems due to lack of nutrition

Answer 4

Main substrate is glucose which has facilitated diffusion. (Fatty acids are seen in higher numbers in macrosomia)

In the first trimester to around 10 wks nutrition is delivered through endometrial gland secretion. This has consistent growth and organogenesis.
However when uteroplacental circulation established, there can be problems with haemotrophic nutrition:
Due to
1. metabolic and endocrine status of uterine blood from mother
2. Blood flow from mum to bb and subsequent transport and metabolism
3. Blood flow through the umbilicus and then metabolic and endocrine status of the fetus still plays a role.

Question 5

What are the main fetal hormones involved in growth and what regulates them

Answer 5

1. IGF- insulin like growth factor produced in fetal tissues and placenta, involved in protein anabolism and putting on weight
   It is regulated in proportion to glucose (and amino acids supplied to the fetus)
   AND
2. Insulin: increases glucose uptake, fat deposition, protein anabolism and placental growth + fuel storage - regulates IGF in proportion

Question 6

How does maternal diabetes lead to high birth weight

Answer 6

1. Excessive maternal substrates (glucose,FFA) actively transported across the placenta
2. Fetal pancreas increases insulin production to maintain normoglycaemia
3. Increased substrate + increased insulin = excess fetal growth and fuel storage = Macrosomia (mostly fat + some skeletal)

Question 7

What are the genetic influences on fetal growth

Answer 7

More influence on lean mass, with ethnicity and fetal sex accounting for <20% variance in birthweight

Question 8

What is Maternal Constraint and when is the signal given in pregnancy

Answer 8

Non-genetic/pathological maternal environment factors which limit fetal growth - this signal is given in early pregnancy and affects the total growth trajectory even if constrain is taken away.

eg. the ability to have a large placenta-> more nutrient depends on:
- body habitus, multiple pregnancies, first born,
- adolescent mother, short interpregnancy interval,
- macronutrient imbalance

Question 9

Can you compare the limiters and regulators of fetal growth to post natal growth

Constrained by the … Growth is regulated by … if … is adequate

Answer 9

Fetal: Constrained by maternal environment
Growth is regulated by substrate supply - if endocrine status is adequate

Postnatal: limited by genetic potential
Growth is regulated by endocrine status - if nutrition is adequate

Question 10

What is the weight in grams for v low birthweight and extremely low birthweight

Answer 10

v Low: <1500 g

Extremely low: <1000g

Question 11

In what order is fat , lean tissue and skeletal growth decreased in accretion in FGR and increase in Macrosomia

Answer 11

FGG it is lost, Macrosomia it is gained in this order

1. Fat (mostly
2. lean tissue +/- skeletal growth

Question 12

What is the relationship between SGA and FGR babies on the bell curve

Answer 12

Any baby less than 10th percentile is SGA

If you are SGA then you are more likely to be FGR as well, however there are some that are not FGR.
There are some that are FGR but not small as well

Question 13

What are the consequences of FGR in the pregnancy and neonatal period

Answer 13

Pregnancy

• preterm birth
• asphyxia
• still birth

Neonatal period

• Asphyxia/Neonatal Encephalopathy
• Hypoglycaemia
• Polycythaemia
• Death

Question 14

What is gestational diabetes

Answer 14

Maternal glucose intolerance developing in pregnancy which predisposes LGA/macrosomia.
The incidence is rising worldwide with the increase of obesity.