The process of taking cells from an embryo to check the number of chromosomes or to test for a specific genetic abnormality.
Preimplantation Genetic Screening (PGS) testing is performed on site at Fertility Tasmania, meaning your embryos do not need to travel. This advancement in technology allows IVF scientists to confirm the correct genetic material (number of chromosomes) is present in an embryo being transferred into the woman. The presence of extra or missing chromosomes is known as aneuploidy and may explain an embryo’s failure to establish or maintain a pregnancy.
Screening for aneuploidy before an embryo transfer increases the likelihood of selecting the embryo(s) with the best chance of implanting while also reducing the rate of miscarriage or chances of a pregnancy of a baby with a genetic condition.
How is PGS performed?
Patients are required to undergo a standard round of IVF. This is where the woman’s ovaries are stimulated through medication to increase the number of follicles that may contain an egg. Over the course of approximately 10 days she is monitored with blood tests and scans to track follicle development. Under sedation the eggs are collected, and later that day fertilised using the male partner’s sperm. Over the course of five days the egg and sperm are monitored to watch for fertilisation and development. For all those embryos that make it to a stage called Blastocyst on day five, they will be assessed for appropriateness for PGS
PGS is where under microscope a very fine laser creates a little hole in the shell of the embryo and a small number of cells are removed from the embryo. These cells are taken from a part of the embryo that goes on to form the placenta. At this stage we cryopreserve the embryo until the results from the testing are made available. These biopsied cells are then used to identify if the embryo contains the correct genetic material.
How does maternal age influence aneuploidy?
Chromosome aneuploidy (abnormal number of chromosomes) is a major cause of IVF failure, pregnancy loss, and in rare cases abnormal pregnancy and live birth. Most aneuploidies arise in the final stages of egg development and increase exponentially with maternal age. The percentage of aneuploid embryos is known to increase with maternal age, however, it may occur in embryos from couples of all ages.
What are the success rates of PGS?
A recent randomised prospective IVF study has shown that selectively implanting euploid (normal) embryos following screening with PGS can increase pregnancy rates by up to 65% (Yang et al, 2012. Molecular Cytogenetics).