Pre-implantation Genetic Screening (PGS),
also sometimes referred to as
Comprehensive Chromosome Screening
(CCS), is a new and important technology
that has revolutionised the world of IVF.
Everyone considering IVF should have PGS
on their radar screen should know the
following facts.
•PGS was developed to address what has
been one of the greatest challenges in
ART, the inability of embryologists to
identify chromosomally normal (euploid)
embryos for transfer into the woman’s
uterus in an IVF cycle. PGS involves
analyzing the cells of the embryo to ensure
that it has 46 chromosomes rather than a
different number. This identiï¬cation is
vitally important to the success of IVF as
chromosomal errors in embryos lead to
their failure to implant, and cause most
miscarriages and all pregnancies involving
chromosomal abnormalities. Only
chromosomally normal embryos become
healthy babies. At least ï¬fty percent of the
embryos of women older than 35 may have
an abnormal number of chromosomes (are
aneuploid).
• In an IVF cycle without any form of
preimplantation genetic screening,
embryologists make their best assessment
of which embryos are chromosomally
normal. They try to inform their
assessment by using a microscope to
visually assess embryo morphology (how
they look). But “eyeballing†embryos under
a microscope is an imperfect method of
assessing which embryos are the best bet
for transfer. Even the most experienced
embryologists are unable to identify
embryos that are chromosomally normal
with their eyes because chromosomally
abnormal embryos often appear to be
perfectly normal.
•In an effort to develop a more precise
method of screening for aneuploidy,
scientists originally developed a technique
called FISH (fluorescent in situ
hybridization). FISH was the ï¬rst technique
to label chromosomes in an embryonic cell,
but the problem with FISH is that only
some chromosome pairs are examined.
The remainder are left unexamined and this
limitation is a signiï¬cant drawback.
• PGS was developed to address the
limitations of FISH. It offers more
“comprehensive†chromosome screening
because all 23 pairs of chromosomes in
each day 5 or 6 (blastocyst stage) embryo
produced in an IVF cycle are examined
following the biopsy of a few cells removed
from the outer layer (trophectoderm) of
each blastocyst.
Chioma Umeha is a Health and Science
Writer/Editor with Independent Newspapers
Limited. She holds a M.A. degree in
International Relations and Strategic
Studies from Lagos State University, B.Sc.
degree in Mass Communication from Enugu
State University of Science and
Technology. She is a multiple award
winning journalist and has attended several
local and international workshops/trainings.
She is a member of the International
Center for Journalists (ICFJ), Nigerian
Union of Journalist (NUJ), Science and
Public Health (SciPH) Journalism Group,
Chartered Institute of Logistics & Transport,
Journalists' Alliance for PMTCT in Nigeria,
Health Writers Association of Nigeria
(HEWAN) among others. On the religious
circle, Umeha is a Sunday School Teacher
and a Counsellor. She is happily married to
Don Umeha and blessed with three lovely
children.
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