Atlanta Center for Reproductive Medicine (ACRM), a Colorado Center for
Reproductive Medicine (CCRM) Network Clinic, has access to a wide range
of genetic screening services, which include preimplantation genetic diagnosis
(PGD) and comprehensive chromosome screening (CCS). By utilizing the latest
assisted reproductive technologies, ACRM’S comprehensive genetic
services optimize fertility care, so patients may achieve their ultimate
goal, a healthy baby.
CCS is a technology which allows us to assess the chromosomes of an embryo.
To understand how CCS works to optimize fertility care, let’s look
at DNA structure.
Chromosomes & DNA | The Basics
Human beings have a total of forty-six chromosomes. Forty-four of these
are called autosomes and are present in both sexes. The final pair is
called the sex chromosomes (X and Y). If an embryo has too few or too
many chromosomes, it is not able to survive and make a live birth. Exceptions
do exist, including Down's syndrome (Trisomy 21, which is three copies
of the 21st chromosome). Other exceptions are Trisomy 13 and 18 (3 copies
of chromosome 13 and 18 respectively), where despite being live born,
these offspring rarely survive more than a few months due to severe birth
defects. Some cases of too many or too few sex chromosomes, such as Turner's
Syndrome where there are only 45 total chromosomes (only one X) and Klinefelter's
Syndrome where there are 47 total chromosomes (two X’s and one Y),
are able to survive.
What is Comprehensive Chromosome Screening (CCS)?
CCS allows us to determine, at the embryo stage, how many chromosomes are
present and therefore whether the embryo has the potential to make a live
birth. This technology allows us to identify embryos that may be able
to establish a pregnancy, such as Trisomy 16 or Trisomy 22, however, but
have a 0% chance of making a live birth and will always result in miscarriage.
How is CCS Different from PGD?
CCS allows us to assess the chromosomes of an embryo and therefore serves
as a screening tool. PGD (Pre-implantation Genetic Diagnosis) allows us
to see if an embryo has a specific disease. For example there are lethal
diseases, such as Tay Sachs Syndrome, which are recessive gene diseases.
This means that the parents were carriers of the abnormal gene, but since
they had a normal gene on the other chromosome, they do not have the disease.
If two carriers reproduce, one quarter of the offspring will inherit the
abnormal gene from each parent and therefore will have the actual disease.
PGD allows us to determine whether a specific embryo carries no copies,
one copy or two copies of the abnormal gene (i.e. normal state, is a carrier
or actually has the disease). PGD is useful when we know exactly what
disease we are looking for. It is a truly diagnostic test whereas CCS
is a screening tool.
Who Should Consider CCS?
CCS is extremely useful for couples that are at risk of chromosomal problems.
The broadest category would be older parents, typically late 30s and older.
It is very clear that older women (and this applies to older men as well
although at a lower rate) are at an increased risk for miscarriages and
Down's syndrome. CCS allows us to identify which embryos are chromosomally
abnormal. CCS is useful for couples that may have had multiple unexplained
miscarriages because we would be able to get a better sense of whether
miscarriages are caused by abnormal embryos or an abnormal uterine environment.
CCS also sheds light on couples who are not responding to routine fertility
treatment and have had repeated failure.
How Does CCS Increase IVF Success?
CCS allows us to exclude abnormal embryos that have no chance of making
a healthy baby. This will reduce the number of embryo transfers necessary
to find the “right embryo.” In this fashion, it will increase
the efficiency of the process and the success of in vitro fertilization
(IVF). Also, since we have ruled out the abnormal embryos, the embryos
which CCS has shown to have a normal number of chromosomes are far more
likely to implant. Therefore we can remain conservative, and transfer
just one embryo at a time, thereby eliminating the risk of a multiple
IVF with CCS Success Rates
IVF by itself is already an extraordinarily powerful tool in reproductive
medicine. Whereas the normal human fecundity rate (likelihood of pregnancy
per cycle) is ~20%, IVF fecundity rates are almost twice as high as that
(when we average all ages together). IVF with CCS rates are higher yet,
surpassing 60% because we can further fine-tune the process of identifying
which embryos to consider for transfer into the uterus.
For more information about CCS, or to schedule a New Patient Appointment
please contact ACRM by calling 678.841.1089, or