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Archive for the ‘CCS’ tag

The Difference Between Genetic Carrier Screening and Comprehensive Chromosome Screening

By Satu Kuokkanen, MD, PhD

June 6th, 2016 at 12:35 pm

image: cooldesign/

Many infertility patients want to know the difference between genetic carrier screening and comprehensive chromosome screening (CCS), as well as why we perform these screening tests.


Genetic carrier screening refers to testing of one or both partners for a large scale genetic carrier status of select conditions that often result in severe early childhood diseases in their offspring. Some examples include cystic fibrosis, sickle cell anemia, and spinal muscular atrophy.  It is important to know that these devastating conditions are rare in the general population; however, some of them cluster in certain ethnic backgrounds or geographical regions.


Most diseases tested are inherited in recessive fashion, which essentially means that a person will need to have two mutated copies of the gene (one inherited from each parent) to actually get that disease. On the other hand, the carrier status by definition indicates that a person has only one mutated gene of the disease in their genome (DNA) and therefore will never contract the disease, but can pass this mutated gene to their offspring. This situation becomes particularly problematic if both partners are carriers for the same condition because, in such case, each of their offspring will have 1 in 4 or 25% risk of getting that disease. Thus, genetic carrier screening attempts to identify parental carrier status prior to pregnancy to avoid conception with a fetus with severe disease(s).


If both parents are carriers for the same genetic condition, the couple can proceed with in vitro fertilization (IVF) in combination with preimplantation genetic diagnosis (often referred as PGD) to essentially weed out affected embryos. Performed on the embryos created after fertilization, PGD tests the embryos for specific gene mutations, prior to transferring any embryos back to the woman’s uterus.  Theoretically, in such scenarios 1 in 4 of the embryos are affected and the rest should be unaffected for the tested condition. The unaffected embryos are transferred to the female partner’s uterus in the hope of establishing a healthy pregnancy.


On the other hand, Comprehensive chromosomal screening (CCS), also known as preimplantation genetic screening (PGS) refers to the testing of an embryo’s numeric chromosome component and can be done as part of IVF whether a couple is concerned about genetic diseases or not. Normal female chromosome component is 46, XX and male 46, XY.  Some conditions typically screened for through CCS are Down’s syndrome (extra chromosome 21) and Turner syndrome (missing chromosome X).


When CCS is elected, embryos are cultured to day 5, the blastocyst stage, allowing biopsy of a number of cells from each embryo.  The numeric chromosome component of each embryo is then analyzed, thus providing the selection of embryos with normal chromosome numbers for transfer. The improvement in pregnancy rates with CCS makes an elective single embryo transfer a feasible option for many patients, thereby avoiding multiple pregnancies and associated adverse maternal and fetal effects.


Importantly, the patients who need genetic carrier screening for specific gene mutations, such as cystic fibrosis, can have their embryos simultaneously analyzed for CCS from the same biopsy.


In addition, CCS includes the sex chromosomes: X and Y. When the chromosome screening results of the embryos are available, the information on sex chromosomes becomes optional for patients. Patients can either elect to transfer embryos of a particular gender or may decide not to know the gender of their embryos.


As the field of genomics continues to evolve, the ongoing research and clinical trials will provide more information on how and to what extent CCS and other tests can be applied to improve IVF outcomes and establish healthy pregnancies for our patients.


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Have you considered genetic carrier screening or comprehensive chromosome screening?



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IVF and Comprehensive Chromosomal Screening (CCS) a/k/a Pre-embryo Genetic Screening (PGS)

By David Kreiner MD

January 20th, 2016 at 1:55 pm


credit T. Minella

In 1985, when I started my fellowship training at the Jones Institute, IVF technology was so new that we numbered each baby that was born as a result of IVF and it was still in double digits. People came to us for IVF from all over the world because our success rate was the best — at that time, just 15 percent.

The technology of IVF was so inefficient then, it was routine to transfer six embryos at a time. That’s what it typically took to create a singleton pregnancy. Sometimes the result was multiples. My experience with multiple pregnancies in those early years opened my eyes and heart to the additional struggles that accompanied patients’ tremendous joy at finally being pregnant.

With the discoveries and improvements in both clinical and laboratory procedures and techniques in the early 2000’s, success rates for IVF boomed… allowing for the transfer of a much more limited number of embryos that depended on patient age and embryo quality. Ultimately, the goal was Single Embryo Transfer (SET), the transfer of one high quality embryo to eliminate the additional risks associated with multiple pregnancies.

The challenge has been that, despite the transfer of an embryo that appeared of highest quality, one could not tell by simply looking under the microscope that the embryo was genetically normal. Abnormal embryos were not just less likely to implant, but if they did, would miscarry or result in an abnormal fetus.

Technology to test embryos with CCS to determine if they were chromosomally normal before transferring them into the uterus has been available for over 10 years but previously the test was often inconclusive, occasionally inaccurate, and potentially hazardous to the embryos. In addition, the test cost between $5000 and $7000. Today, CCS (also known as PGS) has improved to the point that it is nearly 100% accurate and rarely inconclusive or damaging to embryos and the cost is generally not significantly more than $3000, depending on the number of embryos tested.

Incorporating CCS/PGS into IVF will increase the ability for a patient to achieve a live birth of a normal healthy baby while minimizing the risk for a miscarriage and to do so in fewer embryo transfers since only normal healthy embryos need be transferred. It is envisioned that the additional cost of PGS will be offset by virtue of going through fewer frozen embryo transfers .

These 30 years, I have seen a number of game changers in IVF.  CCS/PGS may be among the most significant.

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Would you consider using CCS/PGD?

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