CCS Q&A With Dr. Alison Zimon
QUESTION: What is CCS?
ANSWER: Comprehensive Chromosomal Screening, or CCS, involves testing of embryos at the blastocyst stage to determine whether an embryo has a normal or abnormal number of chromosomes. In humans, many embryos are “aneuploid” meaning they have an abnormal number of chromosomes and this increases drastically with maternal age. Aneuploid embryos cannot result in a normal live birth and instead either fail to implant or lead to miscarriages and chromosomally abnormal pregnancies such as Down Syndrome. CCS, which involves removing a few cells from the embryo at the blastocyst stage, allows the selection of normal or “euploid” embryos prior to transferring them to a woman. Thus, by using CCS and identifying normal embryos for transfer, we can spare patients the otherwise significant risks of failed implantation, miscarriage and fetal aneuploidy, and ultimately increase the overall chance for successful live birth.
- QUESTION: What technological advances in the last several years have led to major increases in the success and utility of CCS?
ANSWER: The method of testing chromosomes has improved drastically. In the past, we used a technology called FISH (Flourescence in situ hybridization) that only allowed the testing of a subset of all chromosomes and was less accurate. The current technology, Next Generation “Next Gen” Sequencing uses gene sequencing and allows comprehensive screening of all 23 chromosomes. While not without limitations, the new technology is highly accurate.
These technological advances in testing embryo chromosomes have coincided with marked advances in embryo culture success. By providing enhanced support to embryo growth, we see more embryos both developing and available for testing, and thus increase the probability of achieving high quality normal embryos which then increases the overall chances for pregnancy and live birth.
Finally, the methods of preserving embryos via a rapid freeze or “vitrification” technology have advanced greatly and thus we see much higher rates of survival after “warming” embryos than we had with the older techniques. Because embryos tested by CCS are typically frozen and then later thawed and transferred if normal, improved vitrification is critical to maximize a successful outcome after CCS.
- QUESTION: Who are candidates for CCS?
ANSWER: Many people seeking reproductive care are ideal candidates for CCS. These include women over the age of 35 years, patients with recurrent pregnancy loss or recurrent implantation failure, and patients with prior unsuccessful fertility treatments. Because CCS enhances the ability to select the most successful embryo, it is a great approach for patients planning single embryo transfer for elective or medical reasons. Also, CCS is a great adjunctive treatment for patients who are already already testing embryos for genetic disorders, such as cystic fibrosis. Finally, any patient who seeks to maximize their success for any embryo transfer and shorten the time to live birth can be considered as reasonable candidates for CCS.
Question: What are the advantages of CCS?
- ANSWER: The advantages of CCS are significant. These include increased probability of live-birth with elective single embryo transfer, reduced rates of multiple pregnancy, and lower pregnancy loss rates. In addition, CCS provides enhanced information about the potential for pregnancy in cryopreserved embryos. CCS testing achieves a reduction in unsuccessful embryo transfers and thereby is associated with fewer fertility treatment procedures per live birth. Overall, CCS shortens the time interval from treatment start to ongoing pregnancy and live birth.