Comprehensive Chromosomal Screening (CCS)
Comprehensive Chromosomal Screening (CCS) is a term used to describe a specific way to select embryos in an IVF treatment cycle. It is also known as Pre-Implantation Genetic Screening (PGS).
CCS involves removing five to six cells from a Day 5 embryo, freezing it, and sending the cells to a genetics lab to test for the number of chromosomes in that embryo.
The test results are then used to determine which embryo to transfer in a frozen embryo transfer treatment cycle in the future.
The aim of CCS is to select the best embryo for a single embryo transfer. The major reason an IVF cycle fails is because the embryo stops growing inside the uterus due to the fact that the embryos have an abnormal number of chromosomes.
As women get older, the proportion of eggs to embryos that are abnormal increases. The usual approach to treating older women in IVF is to transfer more embryos and play the odds. The chromosomal test identifies which embryos are normal – allowing for the transfer of at least one normal embryo. This reduces the risk of multiple pregnancies.
CCS can also help to avoid a failed transfer, miscarriage or a pregnancy complicated by an abnormal fetus such as Down’s Syndrome.
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How much does CCS help?
If an embryo is genetically normal, the chance it will result in a pregnancy is 60 to 70 percent. The risk of miscarriage is about ten percent.
How much CCS helps you depends on your age:
|Woman’s Age||< 30 years||35 years||40 years||> 40 years||> 44|
|IVF pregnancy rate||60%||50%||35%||25%||10%|
|Natural miscarriage risk||10%||20%||30%||40%||50%|
|Risk of pregnancy with chromosomally abnormal fetus||1/500||1/270||1/80||1/60||1/10|
For an older patient, CCS decreases the chance of miscarriage and increases the predictability of conceiving. However, about 30 percent of women 40 and over undergoing CCS will not have an embryo transfer because there won’t be any normal embryos.
How accurate is CCS?
The present technology that tests the DNA in an embryo has an error rate of three to seven percent. It is still recommended that prenatal genetic screening such as CVS or amniocentesis be performed during a pregnancy.
What are the risks?
When PGS was first introduced it was with an embryo biopsy on day 3 using an older DNA technology. It took ten years and 13 randomized clinical trials to show that initial approach didn’t work.
The new approach to biopsy at the day 5 stage embryo and newer DNA technologies hold the promise of better outcomes.* The lower miscarriage rate is reassuring and the incidence of birth defects is not increased over that of regular IVF babies.
*This new approach has been used for less than five years and well-designed and well-executed randomized clinical trails have not yet been completed.
What are the costs?
CCS may add up to $7,000 to an IVF cycle. The additional costs are due to the work of the embryo biopsy, freezing, the costs of the genetic testing and the added cost of a frozen embryo transfer.
So who should use CCS?
It depends on the woman’s age whether she is best suited for CCS. Also, risk level and how strongly she wants to avoid facing a decision about terminating an abnormal pregnancy are factors to consider.
Most physicians agree that patients under the age of 38 are lower risk and that the cost and invasiveness of the procedure are not justified for women 37 years and younger.
At RSC, single embryo transfer has been encouraged and for women 37 years and younger who have a good quality day 5 embryo and the pregnancy rate has been consistently 60 percent without CCS.