Comprehensive Chromosome Screening is a technique usedin parallel with IVF treatment to select
embryos with the right number of chromosomes. After in vitro fertilization, a small number of cells
from each embryo are biopsied and sent to the genetics lab for testing.
The purpose of chromosome screening is to analyze, select and transfer only embryos that have the
normal number of chromosomes. It is known that aneuploidy – any embryo with too many or too
few chromosomes – is the cause of over 60% of miscarriages and a most likely reason for failure to
achieve pregnancy during an IVF cycle.
Preimplantation Genetic Screening (PGS), also known as aneuploidy screening, using Next
Generation Sequencing (NGS) is widely used to select competent embryos, free of chromosome
abnormalities, for embryo transfer. This embryo selection improves clinical outcomes by achieving a
higher implantation rate and a reduction in miscarriage rates.
Who is suitable for Comprehensive Chromosome Screening?
Women 35 years of age or older
Women with a history of repeated miscarriage
Women with a previous pregnancy involving a chromosome abnormality
Woman who have had multiple failed IVF cycles or implantation failure
What methods are available?
FISH (Fluorescent in situ hybridization) requires removal a single cell on Day 3 or several cells on day
5 or 6 of embryo development. The FISH test is done using fluorescent probes that bind to certain
specific chromosomes. The 5 probe FISH method screens for the five important chromosome which
includes X,Y,13,18 and 21.
Next-Generation Sequencing (NGS) is the latest technology in genetic testing all 23 pairs
chromosomes and sex chromosome at a more comprehensive level and with high resolution. NGS
provides the ability to screen embryos from chromosomes errors such as Down syndrome and other
similar aneuploidy conditions.
The procedure has been designed and tested to help couples reduce the risk of conceiving a child in
situations where there is a high risk of a chromosome or genetic disorder.
Preimplantation Genetic Diagnosis (PGD) is the technique of checking the genes or chromosomes for
a specific genetic condition.
Like PGS testing, PGD is also used in parallel with an IVF treatment cycle. A small number of cells are
removed from the blastocyst embryo and sent to the genetic lab for testing.
There are over 100 known genetic disorders that can be tested. For some couples with a less
common genetic disorder, the genetics lab can perform feasibility testing to ascertain if a test can be
developed for their specific disorder.
Who is suitable for PGD testing?
Carriers of sex-linked genetic disorders
Carriers of single gene disorders
Carriers of translocations
Preimplantation genetic diagnosis involves using assisted reproductive technology also known as
ART, a system also used to assist couples with fertility problems. ART is a very delicate and
complicated procedure that considerably increases successful problem free child development
during and after pregnancy.
The procedure is used six days subsequent to egg collection. New embryos are given six days to
develop at which point several cells are selected and removed from each embryo for testing. During
these tests doctors will carry out investigations into the chromosomes or DNA in order to determine
whether or not there are any chromosome or genetic abnormalities evident.
Once tests have revealed the strongest embryos with no chromosome or genetic abnormalities,
these embryos will be transferred to the uterus. At this stage of the procedure the desired outcome
is for the embryos to implant and as a result of implantation pregnancy follows. Using this procedure
the baby will be free of all disorders tested for subsequent to day six of fertilization.