Understanding Comprehensive Chromosome Screening

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One of the newest and most exciting technologies to affect fertility treatment in recent years is Comprehensive Chromosome Screening (CCS), also called Preimplantation Genetic Screening (PGS).

While the idea of screening chromosomes may evoke images of genetic engineering and science fiction, the technology is far more down to earth. It’s also allowing patients to have healthy babies when they couldn’t before.

How Does CCS Work?

By using in vitro fertilization (IVF), it is possible to harvest multiple eggs and fertilize them outside a woman’s body. The resultant embryos develop for a few days into a cluster of cells called a blastocyst. From there it is possible to biopsy several cells in order to test its DNA to “count the chromosomes” to ensure it contains the correct number (23-pairs for humans).

These selected embryos are most likely to result in a healthy pregnancy. If more than one healthy embryo is available, then most patients opt to cryopreserve them and thaw them in the future for another opportunity to conceive.

When is CCS/PGS Used?                   

Because this is a new technology, I often find that there are questions about when and how this can and should be used.

To help clear up confusion, I’d like to address the several scenarios where CCS/PGS is recommended.

One Embryo – One Baby: The Gold-Standard for IVF Success

One of the most significant factors affecting the chances of a successful pregnancy with in vitro fertilization is the viability of the embryo. Historically, it has been difficult to select which embryos are healthiest to replace into the uterus. Decisions were made primarily on embryo appearance (i.e., grade) and/or stage of development (i.e., blastocyst). To resolve the tension between choosing the “best” embryo while maintaining high pregnancy rates, multiple embryos are transferred into the womb.

By evaluating an embryo’s chromosomes, CCS/PGS enables a more perfected way of selecting the healthiest ones. This strategy maintains high pregnancy rates, while mostly eliminating the need to transfer more than one embryo and the risks of a multiple gestation pregnancy. Ultimately, CCS/PGS allows us to choose one embryo at-a-time to help ensure a healthy pregnancy and child. Any remaining embryos may be used for a future opportunity to conceive.

Time-to-Conceive, Age, and Family Building

The time that a couple takes to conceive a successful pregnancy is important for several reasons. First, age is a major contributing factor of infertility, due primarily to the age of the egg (and the sperm, but to a lesser extent). Thus, a longer time to conceive affects the likelihood of success, and ovarian aging continues.

Second, dropout rates are high among couples pursuing fertility treatments due to the demands of treatment, disappointment, and cost.

Last, the option for future fertility is affected by the time it takes to carry and recover from a pregnancy. Even if a woman is successful she will lose time and chances for a subsequent pregnancy. However, if chromosomally viable embryos are stored from a younger age, then they can be used later to maintain equally high pregnancy rates comparable to when they were created.

Reducing Miscarriage and Abnormal Pregnancies

Many women have suffered pregnancy loss, often the result of aneuploidy; a condition where the embryo cells have too many or too few chromosomes. An example is Trisomy-21 that results in Down’s Syndrome if the child is born. In many of these cases, the embryo will not be able to develop normally and the pregnancy may end in miscarriage. While it can affect women at every age, it becomes increasingly common for women older than 35 years, primarily because older eggs are more likely to produce such errors.

For these patients CCS not only helps couples achieve a healthy pregnancy, but it can save them the time and heartache that comes from repeat pregnancy loss.

Testing for Heriditary Genetic Conditions (PGD)

In addition to screening embryos for aneuploidy (PGS/CCS), there are additional tests that can be performed on the biopsied cells to identify rare genetic conditions when one or both parents are a carrier. This procedure is called Preimplantation Genetic Diagnosis (PGD). It can be used to help identify which embryos are affected, unaffected, or a carrier for a disease. The most common conditions are single gene disorders such as cystic fibrosis and tay-sachs. Additionally, testing may be done to eliminate gene mutations leading to cancers, such as BRCA gene mutations (causing breast or ovarian cancer).

Using PGD is only recommended after a couple has had a genetic screening and know that they both have a 25 percent chance or higher of being a carrier of such conditions.

Other Concerns

One concern that many patients have is whether or not CCS can damage an embryo during the biopsy procedure. While there is always risk with any kind of surgical procedure, when this technique is combined with embryo freezing, the chances of the embryo successfully implanting are greatly improved.

Another ethical concern that has emerged with the growth of this technology is that parents may use it simply to select the gender of their child. While a recent international survey indicated that 2 percent of 27,000 couples opted to use CCS to select the gender of their child, the vast majority of patients opt to use this technology for the reasons given above. Most are happy to have a healthy baby, regardless of the gender.

If you have questions, or if you’d like to learn more about me or my practice, schedule your new patient consultation today or call us at (949) 706-2229.