Embryos with the usual number of chromosomes, also called euploid embryos, have a greater chance of becoming a healthy pregnancy and baby. Euploid embryos have 46 chromosomes and are created when a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes. Sometimes embryos are created that do not have the usual number of chromosomes. These embryos, also called aneuploid embryos, are more likely to result in in vitro fertilization (IVF) failure. Aneuploidy also contributes to miscarriage and can be associated with health problems during pregnancy or following delivery. One of the most common examples of aneuploidy is trisomy 21, also referred to as Down syndrome, which is caused by the presence of a third copy of chromosome 21.
What is Preimplantation Genetic Testing for Aneuploidy (PGT-A)?
PGT-A is designed to identify which embryos have the correct number of chromosomes and thus have the greatest potential for a successful pregnancy.
Embryos with the normal number of chromosomes are called euploid embryos. Euploid embryos have 46 chromosomes and are created when a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes. Sometimes embryos do not have the correct number of chromosomes (aneuploidy). Studies by Juno Genetics and its collaborators have shown that transfer of embryos diagnosed as having aneuploidy failed to deliver healthy babies.
Aneuploidy is a common cause of miscarriage and can be associated with problems in a developing pregnancy. The prevalence of aneuploidy increases with maternal age. One of the most common examples of aneuploidy is trisomy 21, also referred to as Down syndrome, which is caused by the presence of a third copy of chromosome 21.
What is PGTseq-A?
Aneuploidy screening through Juno Genetics utilizes targeted next-generation sequencing (tNGS). PGTseq-A has been developed following extensive analytical and clinical validation studies and identifies whole chromosome aneuploidy (extra or missing whole chromosomes). PGTseq-A is greater than 98% accurate in screening for whole chromosome aneuploidy. PGTseq-A also can detect some cases of segmental aneuploidy.
What is segmental aneuploidy?
Segmental aneuploidy refers to extra or missing genetic material from a part of a chromosome rather than from the whole chromosome.
In an internal study where embryos had multiple biopsies performed, the segmental aneuploidy was identified in approximately 50% of rebiopsy samples. Studies have also shown that embryos with segmental aneuploidies can result in a normal pregnancy. However, there have been reports of segmental aneuploidies identified in an embryo biopsy sample that were confirmed to be present in the fetus and resulted in abnormal ultrasound findings.
What is mosaicism?
Mosaicism refers to a potential combination chromosomally normal and chromosomally abnormal cells in a single embryo biopsy sample. Some studies suggest a mosaic result is associated with an increased risk for implantation failure and miscarriage. However, there is no consensus, and these studies are not conclusive. Additionally, embryos with mosaic results have resulted in children who were healthy at birth.
Since the significance of mosaic range results is uncertain, Juno Genetics refers to them as secondary findings of uncertain clinical significance. You and your provider have the option to decide whether you would like Juno Genetics to report results in the mosaic range.
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