parent hopes and prays for a healthy baby. Careful consideration is given
towards the well being of the baby by the mother-to-be for the entire duration
of 9 months. But there are times when you can't stop thinking about the
possible health problems of the baby especially in a high-risk pregnancy.
If you are worrying about this most of the time, you are not
alone. Fortunately, these days, there are numerous tests for pregnant
women which reassure them of the health of the baby throughout their pregnancy.
These tests or the so called 'prenatal diagnostic tests' can identify if the
baby would have certain congenital, genetic, or chromosomal problems. This is
particularly important for a family with a history of a genetic disorder
because the tests may reveal whether the baby is going to have the disorder or
Some genetic disorders are caused
by an abnormal number of chromosomes. Aneuploidy is one of the most frequently observed type of cytogenetic abnormality,
where number of chromosomes is either more or less. Triploidy is a type of
aneuploidy, wherein the individual has three sets of chromosomes instead
of the usual two sets.
In humans, the most common
aneuploidies are trisomies, which are characterized by the presence of one
additional chromosome, bringing the total
chromosome number to 47 instead of 46. The most common human trisomy involves chromosome 21 and is known as
A recent study published in the New England Journal of Medicine evaluated
the accuracy and efficacy of chromosomal microarray as compared to karyotyping
in prenatal diagnosis. A total of 4,406 pregnant women voluntarily participated
in the study. The women were selected based on advanced maternal age, abnormal
result on Down's syndrome screening, structural anomalies on ultrasonography,
and other indications. They were explained the benefits and risks involved in
the chromosomal microarray testing, including the fact that some of the
findings could be of uncertain clinical significance. In both karyotyping and
microarray analysis, fetal cells were obtained via an invasive procedure such
as amniocentesis (fetal cells taken from the amniotic fluid), or chorionic
villus sampling (fetal cells taken from the placenta).
The study revealed that karyotyping and chromosomal microarray
analysis are equally effective in identifying aneuploidies. Microarray analysis reportedly detects
additional clinically relevant information both in cases with structural
anomalies and in those sampled for routine indications, however it did not
identify abnormalities like balanced translocations and triploidies.
The advantage of chromosomal
microarray analysis is its high resolution and sensitivity, which allows
detection of events at the level of genes, as opposed to the level of
chromosomes for karyotyping.
The results of the study showed
that of the 4,406 women who participated in the study, microarray analysis was
successful in 4,340 (98.8 percent) cases. The study thus proved the benefits of
microarray analysis in prenatal diagnosis of genetic abnormalities. However,
like karyotyping, it may also detect abnormalities that do not have any
clinical significance, which would warrant counseling of the patient to remove
any unwanted anxiety.
Chromosomal Microarray versus Karyotyping for Prenatal Diagnosis; Ronald Wapner
et al; N Engl J Med 2012; 367:2175-2184