disorders of fetal growth Flashcards
what is the definition of small for gestational age?
fetus less than 10th centile for age
what is the definition of large for gestational age?
greater than the 97th centile
what is the definition of IUGR?
fetus unable to achieve genetically predetermined size
what is the definition of low birth weight?
birth weight less than 2500grams (can be SGA or premature)
what are the 3 classifications of SGA?
normal small fetus (no abnormalities, normal umbilical artery doppler and liquor, no risk, no special care needed)
abnormal small fetus (chromosomal or structural abnormalities)
growth restricted fetus (placental dysfunction - appropriate treatment or delivery may improve prospects)
what percentage of SGA/FGR are just healthy small foetuses?
40% are normal small fetus
40% are growth restricted
20% are intrinsically small - chromosomal abnormality etc
what are the two classifications of fetal growth restriction?
symmetrical
asymmetrical
when does the insult occur in symmetrical FGR?
early in development so it affects growth processes and cell hyperplasia
when does the insult occur in asymmetrical FGR?
later in development - fetal brain disproportionately large compared to liver (>6) when normal is >3 brain:liver
what are the etiological factors for IUGR?
maternal fetal placental OR intrinsic extrinsic
what are the intrinsic factors of IUGR?
chromosomal aberrations
congenital structural defects
constitutional (genetic heritage)
what are the extrinsic factors of IUGR?
maternal-placental-fetal infections uteroplacental perfusion chronic maternal disease substrate availability toxins
what are some maternal causes of FGR?
chronic disease (HTN, collagen vascular disease, renal disease, thyrotoxicosis, advanced DM, hemoglobinopathies)
pre-eclampsia
malnutrition
infection (toxoplasmosis, malaria, rubella, CMV, herpes, syphilis, listeriosis)
maternal drugs/medications (heroin, methadone, cocaine, cigarette smoke, alcohol, cytotoxic drugs, lithium, etc)
what are some fetal risk factors for IUGR?
multiple pregnancy
infections (TORCH, TB, malaria, parvo virus B19)
congenital malformations
extra-uterine pregnancy
placenta or umbilical cord defects
chromosomal abnormalities (trisomy 13,18,21)
what are some placental factors for IUGR?
uteroplacental insufficiency (defective trophoblastic invasion/placentation, maternal insertion of cord, reduced blood flow - pre-eclampsia, TTTS, decreased functioning mass - small placenta, abruption, praaevia post-term placenta)
what are the underlying mechanisms of IUGR?
insufficient gas exchange and nutrient delivery to fetus maternal disease => decreased oxygen carrying capacity (cyanotic heart disease, smoking, haemoglobinopathy) dysfunctional oxygen delivery system (diabetes with vascular disease, HTN, autoimmune conditions) placental damage ( smoking, thrombophilia, autoimmune disease)
when is growth most vulnerable to maternal dietary deficiencies?
during peri-implantation and period of rapid placental development
what is the role of arginine and plyamines in fetal development?
deficiency causes decreases in NOS which causes decreases in embryogenesis, placental angiogenesis and growth, therefore placental-fetal blood flow is decreases and so there is a decreases in nutrient and oxygen supply from mother to fetus resulting in decreased fetal growth and development
what are epigenetic alterations and how do they occur in the fetus?
stable alterations of gene expression through covalent modifications of DNA and core histones, by 2 mechanisms = DNA methylation and histone modification. nutritional status (insult/deficiency) can alter the fetal genome and imprint gene expression leaving a permanent "memory" throughout life
what are the 3 main functions of the placenta?
metabolism
transport
endocrine
what does the placenta transport?
gases = oxygen and carbon dioxide to and from baby
nutrients = glucose, AA, antibodies, bilirubin
drugs
infectious agents = CMV, rubella measles etc
what types of transport are there in the placenta?
intact transport
partially consumed
metabolised
not transported
what are the perinatal implications of IUGR?
increased fetal morbidity and mortality iatrogenic prematurity fetal compromise in labour increased need for induction of labour and c- section 10 x increase in late fetal deaths still birth prematurity (nec, throbocytopenia, temp instability, renal failure, hypos) asphyxia congenital malformations
what are the long term consequences of IUGR?
abnormalities with HPG axis and cardiovascular disease
insulin resistance
metabolic syndrome
what is the thrifty hypothesis?
metabolically deprived developing fetus becomes metabolically programmed for insulin resistance and impaired glucose metabolism
strong associations between FGR and elevated fasting glucose/insulin levels and T2DM
how is IUGR managed?
reduce risk factors
how is IUGR diagnosed?
difficult!
presence of risk factors,
clinically = serial maternal weight, symphysis-fundal height assessment (poor predictor) customised fundal height charts are better take into account maternal height, weight, parity and ethnicity
US = inadequate fetal growth, reduced amniotic fluid index, placental calcification
what is measured on fetal US/biometry?
Biparietal diameter head circumference Transverse cerebellar diameter femur length abdominal circumference ratios estimated fetal weight (EFW)
what surveillance is there for fetal growth?
serial scans non-stress test amniotic fluid assessment umbilical doppler biophysical profile assessment
what are some ancillary invasive tests?
fetal karyotyping
fetal blood sampling
amniocentesis for LS ratio
how can IGRU be prevented?
largely unpreventable
some evidence for: LDA, mini heparin, reduce maternal smoking, antibiotics to prevent/treat UTIs, antimalarial prophylaxis
how is IUGR managed?
fetal surveillance until the risk of demise in utero demise exceeds the risk of delivery and prematurity
define large for gestational age?
fetus above the 90th centile for gestation
define macrosomia?
birth weight >4000grams regardless of gestational age
what is the prevalence of macrosomia?
9-10% >4kg
what are the risk factors for macrosomia?
maternal hyperglycaemia during pregnancy
previous macrocosmic infant
pre-pregnancy obesity/excessive maternal weight
male fetus
post-term gestation
parental height and race
maternal age <20 years
how is birthweight estimated?
symphysis pubis - fundal height
ultrasound
what are the problems f fetal overgrowth?
maternal diabetes
fetal demise
birth trauma - shoulder dystocia
neonatal hypoglycaemia
