Early screening for chromosomal abnormalities-/ Cardiac defects -How??
Q. 1: How important is
record in the repot page of NT sac
on nasal bone, ductus venosus flow and tricuspid
flow?? Ans: The combination of NT and maternal serum free
β-hCG and PAPP-A improves the detection to 90%. But if the nasal bone,
ductus venosus flow and tricuspid flow are included for statistical risk calculation of aneuploidy of
foetus then the detection rate can increase to about 95%
and the false positive rate can be reduced to 3%
:
Q.2: How to calculate NT ?? Point 1:-What is
meant by NT? Ans:- Nuchal translucency (NT) is the
sonographic appearance of a a) collection of fluid under the skin behind the
fetal neck in the first-trimester of pregnancy. The term translucency is
used, The fluid as imaged may be b) septated or not . c) Moreover one has to
ignore whether it is confined to the neck or fluid envelopes the whole fetus.
·
Q.3: What is the relevance of increased Nuchal translucency (NT) as per
gestation age?? Ans: This thickness of sonographic
appearance of collection of fluid under the skin behind the fetal neck in the
first-trimester of pregnancy also offers an indication that fetuses may
have(but not always) chromosomal
abnormalities, cardiac defects and many genetic syndromes the NT thickness is
increased. The defects that can be
suspected from excess NT & blood flow, Nasal bones imaging are such as Down
syndrome, Edward's
syndrome (trisomy 18), trisomy 13 and many other chromosomal
abnormalities as well as heart problems.
This is a statistical possibility of having
such 4 risks like 1) chromosomal
abnormalities, 2) cardiac defects and 3)
many genetic syndromes,. But this scan
finding are risk calculation (screening tets and not diagnostic).
Q. 4: :- What is the detection rate:??---Screening
by NT can detect about 80% of fetuses with trisomy 21 and other major
aneuploides for a false positive rate of 5%.. So put in another way NT alone
misses about 20% aneuploidies.
- Q.5: Which Lab is reliable?? Where to send serum of
pregnant mother for double marker?? Ans:-Measurement of maternal
serum free β-hCG and PAPP-A by laboratories that can demonstrate good
quality assurance performance( dedicated lab) , However , the FMF software for the
calculation of risks.
In addition to the FMF audit, all sonographers are encouraged to perform
their own internal quality assurance on a monthly basis by examining their
NT distribution using the automated
audit module incorporated within the FMF risk calculation software.
- The
name of the sonographer will be removed from the FMF website list of
holders of the Certificate of competence in NT. their FMF software license
will be revoked. In such case the sonographer will need to be retrained
and apply for recertification by attending the FMF internet based course
on the 11-13 weeks scan and submitting the appropriate logbook of images.
A risk calculation program that uses
an algorithm based on scientific evidence. The software companies that use this
algorithm are Astraia
Software GmbH, ViewPoint GE Healthcare and Zeitgeist Health SE.
1.
Appropriate counseling of the
parents.
Q.
6: Why lab is so important ?? Ans: All the Software is important for risk
calculation: A risk calculation program that
uses an algorithm based on scientific evidence. The software companies that use
this algorithm are Astraia
Software GmbH, ViewPoint GE Healthcare and Zeitgeist Health SE.
Q. 6: Why lab is so important ??
Ans: All the Software is important for risk calculation: A risk
calculation program that uses an algorithm based on scientific evidence. The
software companies that use this algorithm Software is for
first-trimester screening for chromosomal abnormalities by a) maternal age, b) fetal
NT thickness and c) maternal serum free β-hCG and d) PAPP-A. e)Multiple pregancy
f) BMI f) spontaneous preg/ ART .g)
maternal diabetes etc. Should the
concerned lab wish to use the additional
markers for chromosomal abnormalities (nasal bone, tricuspid flow and ductus
venosus flow) they may do so but all risk calculation by Software only
- Q.7: How measure nuchal translucency very
correctly? Ans: The screen should be
at least 2/3rd occupied by the foetal head &neck and foetus
should look face up that nape of
the neck is clearly visible. One has to
wait till foetal movement
ceases for a second and to take the
opportunity to then freeze the
image immediately Sonographer must have patience may have for couple
of seconds till CRL is in the straight line(no
bending of foetus) The fetus should be in a neutral position, with the head
in line with the spine. When the
fetal neck is hyperextended the measurement can be falsely increased and
when the neck is flexed, the measurement can be falsely decreased.
Excess nuchal translucency?
More than normal
Head
up
- NT scan :-Tips for fresh
sonologist : Tip 1:
The gestational period must be 11
to 13 weeks and six days. To put in other ways the fetal crown-rump length should be between 45 and
84mm. The date of N T scan is often prefixed with USG center when booking
scan is contemplated.
- Tip 2 : The magnification of the image should be such that the
fetal head and thorax occupy the whole screen. A mid-sagittal view of the
face should be obtained. This is
defined by the presence of the echogenic tip of the nose and rectangular
shape of the palate anteriorly, the translucent diencephalon in the centre
and the nuchal membrane posteriorly. Minor deviations from the exact
midline plane would cause non-visualization of the tip of the nose and
visibility of the maxilla.
- Tip 3: Care must be taken to distinguish between fetal skin
and amnion. The widest part of translucency must always be measured.
- Tip 4: Measurements should be taken with the inner border of
the horizontal line of the callipers placed ON the line that defines the
nuchal translucency thickness - the crossbar of the calliper should be
such that it is hardly visible as it merges with the white line of the
border, not in the nuchal fluid.
- In
magnifying the image (pre or post freeze zoom) it is important to turn the gain down. This avoids the mistake
of placing the calliper on the fuzzy edge of the line which causes an
underestimate of the nuchal measurement.
- Tip 5 : During the scan more than one measurement must be taken
and the maximum one that meets all the above criteria should be recorded
in the database.
- The umbilical cord may be round
the fetal neck in about 5% of cases and this finding may produce a falsely
increased NT. In
such cases, the measurements of NT above and below the cord are different
and, in the calculation of risk, it is more appropriate to use the average
of the two measurements
·
Tip
8:-What are the limitations of of NT scan or double markers in
sera ?? -We the Obstetrician must remember that this test can't diagnose birth defects. It only shows =foetus
has a greater risk than average.Sometimes
test results are combined with a second- trimester screening( Quad serum screening)
. In that case, the concerned woman may not get test results until her second trimester.
Or she may get the results, and then get combined results after the second test
(combined tets) .
·
he first trimester screening
is a safe, optional test for all pregnant women. It's
a way of checking your baby's risk of certain birth defects,
·
--What the Test Does in Double marker ??
·
To tell at the reception of USG center that “I am not in a
hurry. Sonologist Ma’m can call me according to her convince when work load is
less ”:
·
What is double marker?? The screening involves. a blood test
which estimates levels of two substances –e g. 1) pregnancy-associated plasma protein-A
(PAPP-A) and 2) free beta human
chorionic gonadotropin. These are expressed
as Mean of Median (MoM) Again it is an statistical evolution of possible risk. Quite often such serum tests are planned on
the day of N T scan to minimize visits to Lab & Clinic.
·
As mentioned earlier
if she has a booking visit USG done then
(dating scan at 6-8 weeks) at your clinic then planning the date of NT scan & Serum
markers can be fixed up well ahead.
Inform your patients go USG center after lunch as in morning session there is
too rush. You must wait with enough time
and to tell the at the reception counter
that she is not in a hurry and
sonologist can perform N T scan according his/ her convenience., Because it
takes about 10-15 minutes to do a NT scan along with Doppler studies of foetal vessels
and uterine Doppler as well.
·
A special ultrasound,
called a nuchal translucency screening, measures foetal nasal bone as well as
the fluid at the back of foetal neck. A high volume of fluid can be a sign of
problems.
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