What is NIPT?
Screening test-A sample of maternal blood-
tested - to determine if the developing baby
has certain chromosomal conditions.
During pregnancy, some of the DNA from
the baby (fetal DNA) crosses in to the
mother’s bloodstream .These DNA’s carry
genetic information.
This fetal DNA is analyzed during NIPT to
check for certain chromosomes.
cffDNA
Short DNA fragments present in the maternal
circulation
Maternal and fetal components (usually 90% /
10%)
Produced by the placenta and shed into maternal
plasma
Short half-life: fetal fraction cleared hours after birth
Fetal fraction increases with placental mass
Decreases with ↑ maternal weight
History
In 1997 the presence of cell-free fetal DNA
(cffDNA) in the maternal circulation was
reported.
Since 2000- Fetal RhD typing- cffDNA
tested to determine fetal Bl.Grp status
from maternal blood to help and direct
management of Rh isoimmunization.
2008- robust evidence-detection of
cffDNA- Down syndrome
Initial clinical application:
- sex-linked disorders
- Rhesus disease
- monogenic conditions
.
Trisomy 21
• Overabundance of cfDNA fragments
originating from fetal chromosome 21
• Small difference can be detected
through massive parallel sequencing
(MPS)
.
.
Sequencing techniques:
MPS (‘shotgun sequencing’)-
DNA molecules contained in maternal
plasma sample are sequenced at random.
+ potentially be applied for detecting
chromosomal or genetic aberrations
anywhere in the genome
- genomic regions that are not
directly relevant to NIPT are also analyzed
as the sequencing is random.
Selective sequencing(targeted):-
Genomic regions containing the chromosomes at risk of the aneuploidy are selectively targeted for sequencing
+ the sequencing power can be concentrated on genomic regions of interest
- may not pick up other genome aberrations.
What does NIPT test for?
Most NIPT tests will test for common
conditions including
Down syndrome (Trisomy 21),
Edward syndrome (Trisomy 18),
Patau syndrome (Trisomy 13)
and certain sex chromosome problems
Who might want to have NIPT?
Useful for women in the following situation/s:
An ultrasound indicates a problem with the baby’s growth
and/or development
A screening test during the pregnancy has indicated that
the baby is at increased risk of having a chromosome
condition
A previous pregnancy has been affected by a
chromosome condition
Older mothers (aged 35 years or more at the date of
delivery) who are at a higher risk of having a baby with a
chromosome condition
How Accurate is NIPT?
Highly accurate for the chromosome
conditions that it tests for however the
accuracy is not 100%.
There are also differences in the
accuracy, depending on the
chromosome condition. Eg-, Down
syndrome may be more accurate.
>99% of pregnancies affected by trisomy 21,
trisomy 18 and trisomy 13, and
92% of pregnancies with monosomy X
(Turner syndrome).
If other sex chromosome conditions (extra or
missing copies of the X and/or Y
chromosome) are identified they are
reported as incidental findings.
The sex of the baby can be determined with
>99% accuracy .
Error?
Occasionally following testing, no results are
given.
This may be due to there being too little fetal
DNA(<4%) in the mother’s blood or difficulty
identifying fetal DNA in the mother’s blood.
May ask for second sample.
Most companies refund most part of money
if pt chooses not to go ahead.
Sources of error
Early gest age (harmony-10,VCGS-9)
Obesity(low levels-dilution effect?)
Multiple pregnancy(monozygotic-more
accurate)
Placental mosacism(isolated placental
mosacism)
Maternal conditions-malignancy.
RESULTS
Summary
A screening test -early pregnancy to detect Down
syndrome and other chromosome conditions
Test is safe –no risk to mother or baby
Currently only offered through specialist Centre's
at a cost to the patient – no Medicare rebate
NIPT, like all prenatal tests, is optional
Accuracy of NIPT tests is high though not 100%
A definite diagnosis of a chromosome condition in
the baby can only be made following an invasive
prenatal diagnosis test like CVS or amniocentesis.
Two Major providers
Harmony test (ARIOSA DIAGNOSTICS)
$575+30 (collection kit)
Epworth Freemasons Suite 6, 320 Victoria Pde
Melbourne East, Victoria 3002Phone 9417 6788 Fax 9416 1084
Tooronga Village Suite G12-13, 762 Toorak Road
Glen Iris, Victoria 3146
Phone 9822 1411 Fax 9822 1433
Frances Perry House Suite 13, Level 2, 20 Flemington Road
Parkville, Victoria 3052
Phone 9348 2299 Fax 9348 2599
Panorama test ( VCGS) (NATERA diagnostics)
$721(699+22collection & handling fee)
Royal Children’s Hospital (VCGS)
The Royal Women’s Hospital (Suite 6)
Selected St Vincent’s Pathology Collection Centres
(see website: vcgs.org.au)
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