Improved Genetic Screening for Embryos

RMA Lehigh Valley now offers an updated and more comprehensive Preimplantation Genetic Screening (PGS) for patients undergoing in vitro fertilization (IVF). PGS is a process that involves the testing of embryos for comprehensive chromosomal screening (CCS). The Foundation for Embryo Competence (FEC) obtains biopsies from day 5 or day 6 embryos.

Normally, every human has 23 pairs of chromosomes in nearly every cell in the body. There are 22 sets of “autosomes” numbered 1 to 22. The 23rd pair of chromosomes are the sex chromosomes and they are involved in determining the genetic sex of a person (XX is female, XY is male in most scenarios).

The leading causes of miscarriage are due to an imbalance of chromosome numbers in the developing embryo and fetus. In most cases, the loss of at least one of the chromosomes in a pair (referred to as monosomy) or the gain of one of the chromosomes in a pair (referred to as trisomy) are not compatible with life and can lead to implantation failure or miscarriage.

However, some chromosome abnormalities have been reported after birth with severity ranging from mild or moderate symptoms to very severe. Common examples of chromosome abnormalities include Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13) and Turner syndrome (45,X).

CCS looks for chromosome aneuploidy across the 22 pairs of autosomes and the sex chromosomes (X and Y).

NexCCS is currently the most comprehensive test for CCS using next-generation sequencing (NGS) and has an accuracy of over 98%. The testing process may take several days or weeks, therefore embryos need to be cryopreserved until the results are complete.

The NexCCS can detect monosomies and trisomies (including trisomy 13, 18 or 21 and monosomy X). It is more comprehensive than other screening tests because it is able to detect mosaicism and segmental aneuploidy.

Mosaicism exists when some cells of an embryo have a normal number of cells while other cells have monosomies or trisomies. Segmental aneuploidy occurs when portions of chromosomes are duplicated or deleted. Embryos that have mosaicism or segmental aneuploidy have half the implantation rates and it is unknown how healthy a child will be that has these abnormalities.  Therefore, it is advisable only to transfer embryos with the normal number of chromosomes since they have significantly better outcomes.

For more information about NexCCS and IVF please speak with your RMA Lehigh Valley physician or Nurse.

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