What is a Comprehensive Chromosomal Screening?
CCS is a technology that enables us to analyse and monitor the chromosomes of an embryo. To get how CCS is done to optimize fertility care, let’s get informed about 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 enables us to resolve, at the embryo stage, how many chromosomes are present and therefore whether the embryo has the probability to make a live birth. This technology enables 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 enables us to assess the chromosomes of an embryo and therefore serves as a monitoring tool. PGD (Pre-implantation Genetic Diagnosis) enables 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 enables us to resolve 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 monitoring tool.
Who Should Consider CCS?
CCS is very 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 enables 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 enables 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 pregnancy.
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.
Which countries provide CCS?
Most of the countries like Denmark, UK, Russia, Turkey, Cyprus, Georgia, India, Greece, Sweden, Albania, Andorra, Hungary, Romania, Spain, Dubai, France, Italy, Bulgaria, Estonia, Norway, Switzerland, Finland, Azerbaijan.
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