prenatal diagnosis Flashcards
what are the benefits of prenatal screening and diagnosis?
parental reassurance
prenatal diagnosis may allow women to undertake a pregnancy they might not have otherwise undertaken
if abnormality detected =
increased parental options -> further testing, referral, counselling (plan for birth or termination), preparations for special needs child
altered obstetric management
facilitated neonatal management
what are the risks of prenatal screening and diagnosis?
parental anxiety - false positive, true positive
pregnancy complications
pregnancy loss
what are the current screening methods?
integrated prenatal screening = nuchal translucency, PAPP-A, hCG, AFP, uE3, inhibit A
first trimester screening (combined) = NT, hCG, PAPP-A
quadruple maternal serum screening = hCG, AFP, uE3, inhibit A
what is nuchal translucency?
subcutaneous fluid filled space located between back of fetal neck and skin
measured on US between 11-13+6 measurement is not vaild outside this period
NT increases with gestational age
if >3.5mm = diagnostic testing indicated
associated with = trisomy 21,18,13, triploidy and turners syndrome, spontaneous fetal loss
what are the methods of chromosomal evaluation?
non-invasive = fetal cells from maternal blood, preimplantation embryos (PGD) invasive = amniotic fluid (amniocentesis), placenta (chorionic villus tissue), fetal blood
how is amniocentesis performed?
percutaneous 20-23g needle US guided usually 20cc fluid results 2-3 weeks
what are the complications of amniocentesis?
pregnancy loss - 0.3-1% increase risk = if larger needle, multiple needle insertion, discolouration of fluid, high AFP, placental perforation leakage of amniotic fluid amnionitis vaginal bleeding needle puncture of fetus
how is CVS performed?
percutaneous transabdominal with 19-20g needle
how s CVS analysis performed?
direct analysis examines the trophoblast cells of the placenta, results in few hours, greater vulnerability to mitotic error
cultured analysis = examines the fibroblast like cells of the villi stroma 10-14 days, accurately reflect the chromosomes of fetus
what is mosaicism?
true chromosomal mosaicism is when 2 or more abnormal cell lines are detected in 2 or more cultures from the same individual
psuedomosaicism is a term used to describe 2 abnormal cell lines that are found in only one culture
what are the 4 possible conditions of mosaicism?
1 - mosaicism only in placenta not affecting the fetus or placental function
2 - mosaicism only in the placenta not affecting the fetus but alter placental function
3 - trisomy cells are both in the placenta and in the fetus
4 -trisomy cells in the placenta and uniparental disomy in fetus
when does uniparental disomy occur?
when individual inherits 2 copies of a chromosome pair from 1 parent and no copy from the other parent
how does uniparental disomy occur?
loss of chromosome from a trisomy zygote = triatomic rescue
duplication of chromosome from monosomic zygote = monosomic rescue
fertilisation of gamete with 2 copies of a chromosome by a gamete with no copies of the same chromosome = gamete complementation
what are the health concerns in uniparental disomy?
parental imprinting in the case of heterodisomy and isodisomy
unmasking of recessive conditions in some cases of isodisomy
what is non-invasive prenatal testing?
single blood test that uses cutting edge technology to screen pregnant women for chromosome problems as early as 10 weeks
which patients can be offered non-invasive prenatal testing?
maternal age related risk
positive results on maternal serum screening
abnormal ultrasound findings
prior pregnancy with aneuploidy
parental robertsonian translocation involving one of the tested chromosomes
what are the aims of non-invasive pre0natal testing?
reduce exposure of fetus to risk
reduce false positives
enables high detection rate
testing that can easily be offered to all pregnant women
what are the 2 sources of fetal DNA?
fetal cells = require isolation via mechanical/biochemical means
cell free DNA = maternal blood contains both maternal and fetal cfDNA
how does fetal cell-free DNA get into maternal blood?
released through apoptosis - likely arises from cytotrophoblastic cells of placenta
released into bloodstream as small DNA fragments
reliably detected after 7 weeks gestation
undetectable within hours postpartum
how are cell free DNA analysed?
fetal DNA fragments in maternal blood -> cell free DNA fragments are then sequenced -> compare the individual sequenced chromosomes against a reference for analysis
what are the advantages and disadvantages of NIPT?
+ve
reduces unnecessary procedures in borderline high risk women
can give more equivocal risk assessment than any other options offered on NHS
-ve currently not available on NHS costly still classified as screening not diagnostic takes 7-10 days
