- Current prenatal testing includes testing for
chromosome abnormalities mostly limited to chromosomes 13, 18, 21, X and
- Any normal cell in the body has 23 pairs of chromosomes
and any deviation results in diseases like Downs Syndrome and the like
- Scientists have shown that genetic tests aimed at
testing all the chromosomes detect rare trisomies may be suggestive of
miscarriages and other pregnancy related diseases.
testing is used to determine if the unborn baby is healthy inside the womb. It
helps detect birth defects and genetic diseases in the baby before birth. Most
pregnant mothers prefer non-invasive testing like blood tests rather than the
invasive procedures like amniocentesis where fluid is taken from the amniotic
However, in a small number of patients the non-invasive prenatal testing
can be complicated, as they are either
not in accord with the fetal karyotype or the test fails. Scientists have
discovered that instead of testing for the common genetic defects in specific
chromosomes, if all chromosomes are tested rare abnormalities may be identified
that are suggestive of feto-placental diseases. The study is published in the
journal Science Translational Medicine.
testing is done to check the health of the unborn baby. Prenatal genetic
testing is usually only done in case there is a prior issue related to the
pregnancy. Prenatal genetic testing is recommended when there is any of the
- Previous child with a genetic defect
- Increased maternal age
- Family history of genetic disease or affected children
- Miscarriages and abortions
there are a number of methods for genetic testing including amniocentesis and
chorionic villus sampling, these methods are invasive. They require that the
sample, either amniotic fluid or the chorionic villi be taken from the pregnant
mother. These procedures do have a minimal risk of miscarriage or abortion.
‘Extending non-invasive prenatal testing to all chromosomes can detect rare autosomal trisomies that are associated with early miscarriages and other feto-placental diseases.’
women today prefer non-invasive prenatal testing (NIPT) to avoid these risks.
NIPT is the genetic analysis of fetal DNA by collecting maternal blood. The
analysis checks if there are any deviations in the fetal DNA from the normal.
tests include whole genome sequencing, targeted sequencing and microarray
for deletions, duplications, repeats among others. However, the most common is
the count of the chromosomes which is determined by a test called karyotyping.
A normal cell contains 22 pairs of somatic chromosomes and two X chromosomes in
case of a girl and X and Y in case of a boy. Genetic defects are caused due to
any deviation from this number. Trisomies are very common; in this case instead
of a pair of chromosomes, there is three.
The Problem with NIPT:
the increased accuracy of genetic testing when compared to the non-genetic
assays, a small percentage of the fetal DNA from maternal blood tests can be
complicated. This is either due to atypical findings or discordance with the
NIPT typically considers only the chromosomes that are most frequently found to
be abnormal, for example trisomic (triple) - chromosome 13, 18, 21, X and Y.
current study conducted by the National Institute of Health and National Human
Genome Research Institute have showed that extending the NIPT to all the
chromosomes in the cell can detect genetic disorders
that may explain miscarriage and
abnormalities during pregnancy.
Latest Study Findings:
research team studied two independent cohorts. 89,817 maternal plasma samples
were analyzed; of these 72,972 came from the U.S cohort and 16,885 came from
the Australian cohort.
genetic testing of all chromosomes showed several abnormalities, including copy
number variants and deletions, trisomy of the non-target chromosomes was the
single most common finding between both cohorts. Trisomies that were not
associated with the typical target chromosomes including chromosomes 13, 18,
21, X and Y, were called rare autosomal trisomy.
7 was the most frequently observed rare autosomal trisomy in both cohorts
followed by 15, 16 and 22. Clinical data indicated that rare autosomal
trisomies were associated with early miscarriage, in-utero fetal demise,
intrauterine growth restriction etc.
- Pertile,M. D., Halks-Miller, M., Flowers, N., Barbacioru, C., Kinnings, S. L., Vavrek, D.,Bianchi, D. W. (2017). Rare autosomal trisomies, revealed by maternal plasma DNA sequencing, suggest increased risk of feto-placental disease. Science Translational Medicine,9(405). doi:10.1126/scitranslmed.aan1240