fetal disorders and prenatal diagnosis Flashcards
what are the three classifications of fetal disoreders?
chromosomal
structural
immune
what are the numerical chromosomal disorders?
fetus has an extra chromosome
or
the fetus has a missing chromosome
what are the chromosomal fetal disorders which have a nextra chromosome ?
down syndrome ( trisomy 21) Edwards syndrome ( trisomy 18) patau syndrome ( trisomy 13) klinfelter syndrome ( 47 XXY)
what are the fetal disorders in which there is a missing chromosome ?
turner syndrome (45 X)
what is the most common chromosomal disorder with living outcomes ?
down syndrome ( trisomy 21)
what are the risk factors of birthing a baby with down syndrome ?
maternal age above 35
previous children with down syndrome
parent with a translocated gene
what are the physical features of a child with down syndrome ?
excess skin at the nape of the neck separated joints small ears small mouth white spots on the coloured part of the eye : Brush-field spots
what are the more specific features of babies with down syndrome ?
eyes that slant up at the outer corner small ears flat noses short neck most patients have cardiac anomalies
how can we make a diagnosis of Down Syndrome ?
- first an ultrasound needs to be made , looking for the thickness of the nuchal translucency , give that it is more than 3 mm there is a higher susceptibility of down syndrome
- double and triple marker test can be performed
- NIPT ( non invasive prenatal testing) can also be used for screening
but to make a final diagnosis of down syndrome , genetic testing must be performed
what are the risk factors for neural tube defects ?
low serum folate concentration specific drugs such as antiepileptic drugs positive family history diabetic mothers high body temperature obesity
what can NTD be classified into ?
open and closed
what is hydrocephalus ?
excessive accumulation of CSF in the brain
what is the harmful effect of hydrocephalus ?
excessive fluid causes an abnormal widening of spaces in the brain called ventriculomegalia creating a harmful pressure on the brain
what is the most common cause of hydrocephalus ?
gene mutation
what are the symptoms of hydrocephalus ?
large head with a transparent scalp bulging forehead seizures visual problems abnormal reflexes
what is the treatment for hydrocephalus ?
shunt operation to release excess CSF
what is anencephaly ?
when the skull, scalp and the brain dont form properly in the womb
what is the prognosis of a baby with anencephaly ?
baby will only live for a few hours after birth
where are the most commonn spinal defects found ?
lumbar ans sacral bifida
what are the types of spinal defects ?
spina bifida occulta
meningocele
myelomeningocele
at what time during pregnancies fo fetal anomalies happen ?
during the first trimester when organogenesis happens
what is the treatment for spinal defect ?
surgical correction
what are cleft and lip palate?
openings or splits in the upper lip, the roof of the mouth or both
what are the type of abdominal wall defects ?
omphalocele
gastroschisis
what is the difference betweenn omphalocele and gastroschisis ?
- omphalocele the gut presents inside a sac and straight from the umbilicus
- there is no sac in gastroschisis and the exit is next to the umbilicus
what causes mortality in cases of omphalocele ?
cardiac defects
what is the most common and most important fetal immune disorder ?
Rh incompatibility
what is Rh incompatibility ?
it is an excessive haemolysis of fetal RBCs by antibodies that pass through the placenta from maternal blood
what are the causes of Rh incompatibility ?
- rh alloimmunization of an Rh -ve mother with a Rh +ve husband and so having a Rh +ve baby
- sensitization from previous delivery or miscarriage without receiving an anti D injection
- previous transfusion of an Rh+ve blood
what is congenital haemolytic anemia ?
mildest form which results in fetal anemia that develops 2 weeks after birth also called erythroblastosis fetalis
what is icterus gravis neonatorum ?
the commonest and the moderate form
the baby is delivered anemic but will only begin to appear jaundiced after labour by 24 hours
what is kernicterus ?
this develops when the foetal bilirubin level exceeds 20mg as bilirubin crosses the blood brain barrier and becomes deposited in the basal ganglia , which may cause neonatal death
what is hydrops fetalis ?
intrauterine fetal death occurring due to severe hemolytic anemia that leads to heart failure
what sign is seen in ultrasound that may indicate hydrops fetalis ?
buddha sign
what does prenatal screenning include ?
- Rh factor
- indirect coombs test
- maternal serum biochemical markers
- US screening for nuchal translucency
- cell free fetal DNA
what are the maternal serum biochemical markers ?
AFP : alpha fetoprotein which is produced by the yolk sac, fetal liver and GIT
HCG
PAPP-A : pregnancy associated plasma protein A
UE3: unconjugated estriol
what is the double marker test ?
testing for both HCG and PAPP-A together with the ultrasound measurement of the nuchal translucency
when is the double marker test performed ?
at 11-13 weeks ( first trimesteric)
what would be the results of the double marker test for a baby with down syndrome ?
high HCG and low PAPP-A levels
what is the triple marker test ?
the combination of AFP, HCG and UE3 in one test
when is triple marker test performed ?
in the second trimester at 15-16 weeks
what test results in the triple marker test would show a high risk of down syndrome ?
HCG high
AFP low
UE3 low
what would the maternal marker levels be like in trisomy 18 ?
all three markers would be low
in neural tube defects which maternal marker will be raised ?
AFP
when are the anomaly scans performed ?
1st trimesteric ultrasound ( 11-13 weeks)
2nd ( 18-22 weeks)
what ultrasonography findings could indicate down syndrome ?
nose hypoplasia
NT >3 mm
when can cell free foetal DNA be used ?
using PCR at around 10-12 weeks gestation
what is chorionic villous sampling ?
a sample of the placenta is used ( from trophoblastic cells) , this sample can be obtained either trans-abdominal or trans-vaginal , this can be done as early as 11 weeks
what is the risk of CVS ?
2% risk of miscarriage
when can amniocentesis be performed ?
14-16 weeks
what are the risks of amniocentesis ?
small risk of fetal miscarriage
small risk of fetal infection n
rupture of membranes
accidental haemorrhage
what is cordocenteses ?
obtaining fetal blood sample
when can cordiocentesis be done ?
20 weeks gestation
what is the earliest form of testing that can be done in an effort to detect chromosomal abnormalities ?
pre implantation genetic diagnosis when a cell is taken at the 8 cell stage without any subsequent complications to the fetus
