Should a day
come in 22 nd century where routine amniocentesis followed by preservation of
“Amniotic Stem Cells” for later use if warranted??
Prenatal diagnosis is the branch of medicine and in
particular of obstetrics that studies and applies the techniques that reveal the normality or the presence of
disease of various kinds. In the fetus
all the techniques of prenatal diagnosis
are performed during
pregnancy and may be invasive or less. Prenatal
diagnosis of fetal genetic conditions
is a standard part of modern obstetric care. But unfortunately, many of
the current methods rely on invasive
methods (CVS/amniocentesis) and
are associated with an inherent
risk of fetal loss. Consequently there has been a long term
goal for development of NIPD(Non
Invasive prenatal diagnois) . What is cffdna test in maternal
blood? Recently an extremely
sensitive test for the most common aneuploidies and in particular. Down syndrome
has been proposed to be
performed on maternal blood. This test
is based on the count of
fragments of specific chromosomes in maternal blood
although not belonging to
diagnostic tests but to probabilistic
ones this test is absolutely the most accurate
so far available with values around 99.99% sensitivity and 0.2% false
positives . Also ultrasound
in th second trimester of pregnancy that can
detect any malformation or fetal
abnormality and fetal
echocardiography which analyzes sonographically the fetal
heart not only anatomically but
also from the dynamic functional point
of view may be considered methods of prenatal diagnosis. This
technique cannot identify
genetic diseases.
Role
of Molecular genetics ?? Ans:- The phenomenal
developments in molecular genetics and
technological refinements which have occurred over the past
decades have
revolutionized the area of
prenatal genetics , state of the art care
commences with comprehensive preconceptional counseling .
Conclusion:- Prenatal diagnosis is now feasible from the moment of conception onward
. Imaging techniques have allowed non invasive diagnosis
while minimally invasive techniques concentrate on sampling maternal
blood for fetal cells or markers of feto placental metabolism.
Invasive techniques have
been rapidly expanding and becoming safer comprising
of A) chorionic villus
sampling B) early amniocentesis or C)
midtrimester amniocentesis as well as very early fetoscopy
and umbilical vein sampling Advances in prenatal diagnostic
techniques allow for earlier more rapid and more effective detection of congenital disorders
Recent advances in non invasive detection
methods such as fetal
ultrasound and the isolation of fetal cells in the maternal
circulation allow the intrauterine diagnosis
of congenital infections and chromosomal
and Mendelian disorders as well
as hematologic disorders.
We currently have the potential to diagnose a
number of others for which the opportunity has not yet arisen. If A) biochemical B) morphologic C) chromosomal or D) genetic:-deoxyribonucleic
acid alternation is known for a specific condition and is likely to be expressed in one of the
fetal tissues or secretions attempt at prenatal diagnosis is reasonable .
Forget
CS /Lap ports!!!! Know what are gene probes???? Development of specific
gene probes
::Diagnosis of inherited disorders
in utero :-- Our ability to
detect the inherited disorders
in utero will continue to
improve both in the number of specific
disorders successfully diagnosed
or excluded and in the increasingly
earlier stages of pregnancy
at which the disorder can be
detected. Non invasive prenatal testing
and non invasive approach
involves analysis of cell
free fetal DNA in maternal
plasma or serum . Another approach
utilizes fetal cells within
the maternal circulation as a source
of fetal DNA. Advances in instrumentation
have decreased the risk of the
invasive methods of prenatal
diagnosis and improvement in non invasive methods such as maternal serum screening may eliminate the need for invasive procedures altogether
.
Detection
of useful DNA polymorphisms linked to genes for specific diseases and development of specific
gene probes
have improved the accuracy
of diagnosis and reduced the need
for specific fetal tissues.
The entire genome of an individual is present
in each cell even though a specific
gene product may not be expressed
in that cell. Thus DNA
restriction endonuclease studies can be
performed on amniotic fluid
cells chorionic villi fetal
cells in maternal circulation and fetal
tissues with equal facility.
The usefulness of prenatal diagnosis
will always be limited by the
ability to detect pregnancies
at risk. If carrier detection is unavailable the only way to identify couples at risk
for offspring with an
autosomal recessive condition
is by the birth of an
affected child. For autosomal dominant
and X linked recessive and dominant
conditions new mutations will continue to occur. As mentioned previously screening
of all pregnancies for all
defects is not possible now and is unlikely ever to be feasible either economically or technically . The reliability of prenatal diagnosis
will continue to depend upon accurate
diagnosis in the index case and upon the availability of a specific and sensitive test with no overlap in values between
heterozygotes and homozygotes for
autosomal recessive conditions or between normal and affected
fetuses with autosomal dominant and X linked recessive
disorders . Correct
interpretation of test results is subject to experience recognition of artifact
and variation in the expression
of a given disorder in utero.
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