Normal and disordered fetal growth Flashcards
How do you know if a baby is under or overgrown
Assess size at particular point of gestation, compare to spectrum of normality for that time point.
Normal = between 10th and 90th percentile
Define SGA
Small for gestational age
Fetus <10th weight percentile for age
Define IUGR
Intrauterine growth restriction
Fetus unable to achieve genetically predetermined size
Define LBW
Low birth weight
Less than 2500g regardless of gestational age
Can be due to SGA or prematurity
What are the classes of SGA fetuses
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
What is the risk of assessing for SGA
Many normal/healthy SGA fetuses are subjected to high risk protocols and potentially iatrogenic prematurity
What is FGR
Fetal growth restriction, can be symmetrical or asymmetrical
What is symmetrical FGR
Head and body proportionately small
Fetal insult during early development
Affected cell growth and hyperplasia
What is asymmetrical FGR
Fetal brain disproportionately small large compared to liver (normal ratio >3, asymmetrical >6)
Fetal insult during later development
Placental problems common
What is skeletal dysplasia
Distinct growth patterns due to differential impacts on axial and peripheral skeletal growth
What are the classes of causes of IUGR
Intrinsic, Extrinsic
Maternal, fetal, placental
What are the intrinsic causes of IUGR
Chromosomal abberations
Congenital structural defects
Genetic constitution
What are the maternal causes of IUGR
Infection eg. toxoplasmosis, malaria, rubella, cytomegalovirus
Chronic disease eg. hypertension, renal disease, advanced diabetes, haemoglobinopathies
Preeclampsia
High altitude
Malnutrition
Drugs
What are the fetal causes of IUGR
Multiple pregnancy
Infection
Extra-uterine pregnancy
What are the placental causes of IUGR
Uteroplacental insufficiency Defective invasion/placentation Lateral insertion of cord Reduced blood flow to placental bed eg. preeclampsia Vascular anomalies Decreased functioning capacity
What is the underlying mechanism of IUGR
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)
How do we know the intrauterine environment is important in fetal development
Recipient mother is more important for fetal growth than egg donor in embryo transfer
What is the role of maternal nutrition in fetal development
Undernutrition reduces placental and fetal growth
When is fetal growth most vulnerable to maternal dietary deficiencies
During the peri-implantation stage and periods of rapid placental development
What is the molecular mechanism of fetal programming
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
What are the 3 main placental function
Transport
Metabolism
Endocrine
How are nutrients transported across the placenta
Glucose- facilitated diffusion, hexose transporters
Amino acids- active transport
Which antibodies are transported across the placenta
IgG
How is bilirubin transported across the placenta
Conjugated form from mother is poortly transported
Unconjugated from fetus crosses easily
What are the perinatal implications of IUGR
Increased morbidity/mortality- iatrogenic prematurity, fetal compromise in labour, need for induction or caesarian
Stillbirth- due to prematurity, asphyxia or congenital malformations
What are the risks of prematurity
Necrotising enterocolitis Thromocytopenia Temperature instability Respiratory distress syndrome Renal failure Metabolic problems
What is the thrifty phenotype hypothesis
Metabolically deprived fetus becomes metabolically programmed for insulin resistance and impaired glucose metabolism
Strong association between FGR and prevalence of type 2 diabetes
How is IUGR managed
Identify those at risk, diagnosis, surveillance until risk of in utero demise exceeds risk of delivery
How is IUGR diagnosed
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
What are the advantages of customised fundal height charts
Improved sensitivity
Takes into account: maternal height, weight, parity, ethnicity
What does IUGR surveillance entail
Serial scans Non-stress test Amniotic fluid assessment Umbilical doppler Biophysical profile assessment
How are uteroplacental dopplers used in IUGR
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
How are fetal dopplers used in IUGR
Pulsatility index, ductus venosus and short-term variation important indicators for timing of delivery before 32 weeks
Delivery if any parameter becomes consistently abnormal
What ancillary invasive tests are done in IUGR
Fetal karyotyping
Fetal blood sampling
Amniocentesis for lecithin-sphingomyelin ratios
How is IUGR diagnosed neonatally
Low ponderal index
Low subcutaneous fat
Hypoglycaemia, hyperbilirubinaemia, necrotising enterocolitis, hyperviscosity syndrome
How is IUGR prevented
Largely unpreventable by some evidence of benefit for LDA and miniheparin, reducing maternal smoking, antibiotics to prevent UTIs, antimalarial prophylaxis
Define LGA
Large for gestational age
Fetal size >90th percentile for that gestation
Define macrosomia
Birth weight >4000g regardless of gestational age
Timeline for assessing IUGR (detailed)
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
What are the risk factors for macrosomia
maternal hyperglycaemia Previous macrosomic infant Pre-pregnancy obesity Male fetus Post-term gestation Parental height + race Maternal age <20 years
What are the problems of fetal overgrowth
Maternal diabetes
Fetal demise
Birth trauma eg. shoulder dystocia
Neonatal hypoglycaemia
