PGT-A (formally Comprehensive Chromosome Screening (CCS)
PGT-A (formally CCS) is the removal and testing of cells from embryos created through the IVF process. By determining how many chromosomes are present in these cells, we can identify the embryos that are most likely to implant in the uterus and result in a healthy ongoing pregnancy.
PGT-A (formally CCS) may also provide some insight into the reason that some patients have had difficulty becoming or staying pregnant. Also known as preimplantation genetic screening (PGS), or comprehensive chromosome screening (CCS), it is the most advanced form of chromosomal screening on embryos.
What does PGT-A test for and what will I learn about my embryos?
PGT-A (formally CCS) counts the number of chromosomes in each embryo’s biopsied cells. Chromosomes are packages of genes, or DNA, within the cells. Humans normally have 46 chromosomes in each cell; 23 come from the sperm cell and 23 from the egg cell. The first 22 pairs of chromosomes are identified by number, 1 through 22, while the last pair reflects the gender of the embryo: XX for female, XY for male. Embryos with the normal number of chromosomes are considered “euploid”, and those with an abnormal number of chromosomes are considered “aneuploid”. Aneuploidy is common in embryos, and can cause failed implantation, miscarriage, or the birth of a child with health problems. A normal chromosome result for a female is 46,XX and for a male, 46,XY. For more background information on basic genetics and inheritance, see our Resources page.
How experienced is ORM in performing PGT-A?
Our embryologists have extensive experience with embryo biopsy, having biopsied over 12,000 embryos between 2010 and late 2016. PGT-A is a routine part of the IVF patient workflow at ORM, with our clinical and laboratory teams having facilitated the process on over 2000 patients to date. About 80% of our IVF patients now choose to do PGT-A with next-generation sequencing as part of their treatment.
What are the steps of a typical IVF cycle with PGT-A?
- In Vitro Fertilization: embryos are created and grown to the blastocyst stage (day 5 or 6).
- Trophectoderm biopsy of ~5-10 cells from the future placental cells of each embryo.
- Results available within 1-2 weeks.
- Transfer embryos to the uterus of the patient or surrogate in a subsequent frozen embryo transfer cycle.
- Extra embryos remain frozen for future use.
What genetic testing technology is used to count the chromosomes?
ORM is proud to have been one of the first IVF clinics in the world to offer PGT-A (formally CCS) using next-generation sequencing (NGS) technology through our PGT laboratory partners.
NGS is a technology that has revolutionized genetic testing and research in virtually all medical specialties. It is a way of sequencing (determining the order of the base pairs, or “spelling “of ) DNA that is more thorough and efficient than previous technologies. NGS can be used to sequence thousands of small pieces of DNA within an embryo’s cells in order to determine how many chromosomes are present in those cells. As NGS evolves it promises to be more efficient, less expensive, and more comprehensive than other genetic testing technologies.