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Genetic Screening: Updates from ASRM

Genetic Screening: Updates from ASRM

This year, a hot topic at the ASRM Annual Meeting in San Diego was comprehensive chromosome screening (CCS), a technique that allows screening of embryos for genetic problems prior to implantation previously known as preimplantation genetic screening (PGS). There were 27 presentations on CCS.

Refinements in techniques

Over the past several years, refinements in techniques have allowed CCS to reemerge as a viable embryo selection tool that improves pregnancy rates of in vitro fertilization (IVF).

• The first technical breakthrough was the ability to culture embryos to day 5–6 of development (blastocyst stage), when embryos are more resilient to biopsy and cells within the embryo are more likely to be consistent.
• CCS has also made the biopsy more accurate. It involves testing all 23 pairs of chromosomes at once by using advanced microarray technology.
• Lastly, rapid embryo "freezing" called vitrification can safely store the biopsied embryos for future use while waiting for testing results.

Better results

In the past few years, researchers presented preliminary—mostly cohort—studies of CCS showing promising results. This year, it was exciting to see a Prize Paper presentation that detailed a randomized control trial (RCT), which is a more rigorous scientific method than a cohort study. It compared pregnancy rates of traditional IVF to IVF cycles using CCS and subsequent frozen embryo transfers of normal embryos.

In this study, CCS produced clearly superior results than traditional IVF:

• Better pregnancy rates by about 50 percent (60.8 percent vs. 40.9 percent)
• Fewer embryos transferred (1.7 vs. 2.2)
• Lower pregnancy loss rate (0 percent vs. 20 percent).

Another interesting study confirmed our anecdotal experience showing that embryo morphology is not a good predictor of normal embryos. In this study, 41 percent of the “best” embryos selected by traditional morphology turned out to be chromosomally abnormal using CCS.

Also an RCT, a third noteworthy study found that the pregnancy rates of transferring a single CCS-tested normal embryo was equal to that of transferring two of the best embryos selected by morphology (69 percent vs 67 percent). At the same time, it significantly reduced the risk of twins (0 percent vs. 58 percent).

PFC's experience

In an article published in the last issue of Fertility Flash, I presented PFC’s experience with CCS. Our average implantation rates are 76 percent for women under the age of 40 and 60 percent in those older than 40. From biopsy and vitrification, we have been able to recover greater than 97 percent of the embryos.

It has been exciting to be at the forefront of technological advances in genetic screening and to be in such good company with other well-respected experts in our community.

- Liyun Li, MD

View Dr. Li's Google+ Page »

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