What is Comprehensive Chromosome Screening (CCS) & How Does it Increase IVF Success?

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 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.

For more information about CCS, or to schedule a New Patient Appointment please contact ACRM by calling 678.841.1089, or click here.

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