Normal and disordered fetal growth

Question 1

How do you know if a baby is under or overgrown

Answer 1

Assess size at particular point of gestation, compare to spectrum of normality for that time point.
Normal = between 10th and 90th percentile

Question 2

Define SGA

Answer 2

Small for gestational age

Fetus <10th weight percentile for age

Question 3

Define IUGR

Answer 3

Intrauterine growth restriction

Fetus unable to achieve genetically predetermined size

Question 4

Define LBW

Answer 4

Low birth weight
Less than 2500g regardless of gestational age
Can be due to SGA or prematurity

Question 5

What are the classes of SGA fetuses

Answer 5

Normal small fetus- no structural abnormality, normal umbilical artery. Not at risk, no special care needed
Abnormal small fetus- chromosomal or structural abnormality
Growth restricted fetus- results from placental dysfunction

Question 6

What is the risk of assessing for SGA

Answer 6

Many normal/healthy SGA fetuses are subjected to high risk protocols and potentially iatrogenic prematurity

Question 7

What is FGR

Answer 7

Fetal growth restriction, can be symmetrical or asymmetrical

Question 8

What is symmetrical FGR

Answer 8

Head and body proportionately small
Fetal insult during early development
Affected cell growth and hyperplasia

Question 9

What is asymmetrical FGR

Answer 9

Fetal brain disproportionately small large compared to liver (normal ratio >3, asymmetrical >6)
Fetal insult during later development
Placental problems common

Question 10

What is skeletal dysplasia

Answer 10

Distinct growth patterns due to differential impacts on axial and peripheral skeletal growth

Question 11

What are the classes of causes of IUGR

Answer 11

Intrinsic, Extrinsic

Maternal, fetal, placental

Question 12

What are the intrinsic causes of IUGR

Answer 12

Chromosomal abberations
Congenital structural defects
Genetic constitution

Question 13

What are the maternal causes of IUGR

Answer 13

Infection eg. toxoplasmosis, malaria, rubella, cytomegalovirus
Chronic disease eg. hypertension, renal disease, advanced diabetes, haemoglobinopathies
Preeclampsia
High altitude
Malnutrition
Drugs

Question 14

What are the fetal causes of IUGR

Answer 14

Multiple pregnancy
Infection
Extra-uterine pregnancy

Question 15

What are the placental causes of IUGR

Answer 15

Uteroplacental insufficiency
Defective invasion/placentation
Lateral insertion of cord
Reduced blood flow to placental bed eg. preeclampsia
Vascular anomalies
Decreased functioning capacity

Question 16

What is the underlying mechanism of IUGR

Answer 16

Insufficient gas exchange and nutrient delivery to fetus:
Decreased O2 carrying capacity (cyanotic heart disease, smoking, hameoglobinopathy)
Dysfunctional O2 delivery system (diabetes with vascular disease, hypertension, autoimmune conditions)
Placental damage (smoking, thrombophilia)

Question 17

How do we know the intrauterine environment is important in fetal development

Answer 17

Recipient mother is more important for fetal growth than egg donor in embryo transfer

Question 18

What is the role of maternal nutrition in fetal development

Answer 18

Undernutrition reduces placental and fetal growth

Question 19

When is fetal growth most vulnerable to maternal dietary deficiencies

Answer 19

During the peri-implantation stage and periods of rapid placental development

Question 20

What is the molecular mechanism of fetal programming

Answer 20

Nutritional insult during development leaves memory by altering epigenetic state of fetal genome
Epigenetic alterations in early embryos can be carried forward to later developmental stages
Either DNA methylation or histone modification- methylation or acetylation

Question 21

What are the 3 main placental function

Answer 21

Transport
Metabolism
Endocrine

Question 22

How are nutrients transported across the placenta

Answer 22

Glucose- facilitated diffusion, hexose transporters

Amino acids- active transport

Question 23

Which antibodies are transported across the placenta

Answer 23

IgG

Question 24

How is bilirubin transported across the placenta

Answer 24

Conjugated form from mother is poortly transported

Unconjugated from fetus crosses easily

Question 25

What are the perinatal implications of IUGR

Answer 25

Increased morbidity/mortality- iatrogenic prematurity, fetal compromise in labour, need for induction or caesarian Stillbirth- due to prematurity, asphyxia or congenital malformations

Question 26

What are the risks of prematurity

Answer 26

``` Necrotising enterocolitis Thromocytopenia Temperature instability Respiratory distress syndrome Renal failure Metabolic problems ```

Question 27

What is the thrifty phenotype hypothesis

Answer 27

Metabolically deprived fetus becomes metabolically programmed for insulin resistance and impaired glucose metabolism Strong association between FGR and prevalence of type 2 diabetes

Question 28

How is IUGR managed

Answer 28

Identify those at risk, diagnosis, surveillance until risk of in utero demise exceeds risk of delivery

Question 29

How is IUGR diagnosed

Answer 29

Presence of risk factors Clinical- serial maternal weight, symphysio-fundal height assessment Ultrasound- inadequate fetal growth, reduced amniotic fluid index, placental calcification, fetal biometry Customised fundal height charts

Question 30

What are the advantages of customised fundal height charts

Answer 30

Improved sensitivity | Takes into account: maternal height, weight, parity, ethnicity

Question 31

What does IUGR surveillance entail

Answer 31

``` Serial scans Non-stress test Amniotic fluid assessment Umbilical doppler Biophysical profile assessment ```

Question 32

How are uteroplacental dopplers used in IUGR

Answer 32

Uterine- High resistivity index, notch in pulmonary embolism. High false positive, low positive predictive value Umbilical arteries- Increased impedance to flow in FGR. Absence then reversal and end diastolic flow. Increased incidence of lethal abnormalities. High risk pregnancies should have UA dopplers

Question 33

How are fetal dopplers used in IUGR

Answer 33

Pulsatility index, ductus venosus and short-term variation important indicators for timing of delivery before 32 weeks Delivery if any parameter becomes consistently abnormal

Question 34

What ancillary invasive tests are done in IUGR

Answer 34

Fetal karyotyping Fetal blood sampling Amniocentesis for lecithin-sphingomyelin ratios

Question 35

How is IUGR diagnosed neonatally

Answer 35

Low ponderal index Low subcutaneous fat Hypoglycaemia, hyperbilirubinaemia, necrotising enterocolitis, hyperviscosity syndrome

Question 36

How is IUGR prevented

Answer 36

Largely unpreventable by some evidence of benefit for LDA and miniheparin, reducing maternal smoking, antibiotics to prevent UTIs, antimalarial prophylaxis

Question 37

Define LGA

Answer 37

Large for gestational age | Fetal size >90th percentile for that gestation

Question 38

Define macrosomia

Answer 38

Birth weight >4000g regardless of gestational age

Question 39

Timeline for assessing IUGR (detailed)

Answer 39

Booking assessment during 1st trimester If 3+ minor risk factors or 1 major risk factor the reassess at 20 weeks using PAPP-A (<0.4) or MOM, fetal echogenic bowel If 3 or more minor risk factors uterine artery doppler at 20-24 weeks. If normal, assessment of fetal size and umbilical artery doppler in third trimester If UA doppler abnormal major risk factor then serial assessment of fetal size and umbilical artery doppler from 16-18 weeeks Reassess during 3rd trimester

Question 40

What are the risk factors for macrosomia

Answer 40

``` maternal hyperglycaemia Previous macrosomic infant Pre-pregnancy obesity Male fetus Post-term gestation Parental height + race Maternal age <20 years ```

Question 41

What are the problems of fetal overgrowth

Answer 41

Maternal diabetes Fetal demise Birth trauma eg. shoulder dystocia Neonatal hypoglycaemia