PGD: Preimplantation Genetic Diagnosis / Embryo Biopsy
What is Preimplantation Genetic Diagnosis (PGD)?
Preimplantation genetic diagnosis is a technique in which embryo biopsy is used to evaluate the genetic material of the embryos created through in vitro fertilization (IVF). Cells are removed from each developing embryo for genetic analysis. We offer PGD for single gene defects (Cystic Fibrosis, Spinal Muscular Atrophy, Sickle Cell, Huntington’s) or for genetic markers of cancer such as BRCA1/BRCA2. These are situations where we test for the presence of a specific genetic mutation in each embryo. Using PGD, we can identify the embryos free of genetic mutations to avoid the possibility of having a child that will carry the mutation or have a genetic disease. For PGD, the couple with the genetic defect will need to provide blood for genetic analysis, in order to know what to look for in the embryos.
The biopsy results will take several days, and therefore all of the embryos must be frozen after the biopsy. Once we know which embryos are normal, they can be thawed for use at a later date.
What is Preimplantation Genetic Screening (PGS)?
Preimplantation genetic screening is a technique in which embryo biopsy is used to evaluate the genetic material of the embryos created through in vitro fertilization (IVF). Instead of testing for a specific genetic mutation (PGD), the genetic analysis is performed to look for an abnormal number of chromosomes (aneuploidy) or for a chromosomal translocation, both of which may cause miscarriages.
A normal embryo must have 46 chromosomes in the right combination to enable normal viability – 23 from the mother and 23 from the father. If the early dividing cells do not divide equally and distribute these chromosomes equally and in the right way, then aneuploidy is the result. Aneuploid embryos are very common, and are the most common cause of miscarriages and failure to conceive through IVF. This occurs more often in older women, and is the most significant reason why fertility declines with increasing age. This also explains why chromosomal and congenital anomalies, such as Down Syndrome, also increase with increasing age of the female partner.
Traditionally, embryos produced by IVF are assessed microscopically to predict their viability; as suggested by their overall appearance. PGS goes a step further, by actually screening the genetic information contained within the embryo prior to embryo transfer. Embryos free of aneuploidy can be selected and transferred back to the patient. This increases the chance of pregnancy and reduces the risk of miscarriage. PGS can also be used to select gender if someone is interested in family balancing.
For PGS, embryo biopsy is done on a day 5 or day 6 embryo, then the cells are shipped to a lab for genetic analysis. Next Generation Sequencing (NGS) is performed to search for aneuploidy, translocation, or small deletions or duplications of chromosomal material. The embryos are frozen immediately after the biopsy as the NGS takes a few days to complete. Once we receive the results, the patient will return for a frozen embryo transfer procedure.
PGD/PGS Process at Carolina Conceptions
Preimplantation Genetic Diagnosis continues to evolve, with optimized outcomes at Carolina Conceptions. Through December 2015 we have performed over 300 cases of embryo biopsy, making us the most experienced center for embryo biopsy in the region. In late 2011, Carolina Conceptions began doing only day 5 and day 6 embryo biopsy (blastocyst biopsy), as compared to day 3. This increases the accuracy of PGD/PGS by being able to analyze multiple cells from each embryo, instead of only one cell from a day 3 embryo. This has also been associated with improved pregnancy rates due to the fact that the embryos are more developed and less likely to be injured from the biopsy. In the past year, we have had a 55% implantation rate for chromosomally normal embryos, so we recommend transferring a single embryo at a time. This pregnancy rate is far better than the pregnancy rate typically seen with IVF, especially when we consider that the cases of embryo biopsy included many women in their late 30’s and even some who were over 40. Carolina Conceptions is proud to be one of the first centers in the country to offer blastocyst biopsy. PGD and PGS does add some additional cost to the IVF process and we suggest you speak with our financial coordinators to get details.
For more information about genetic embryo testing, please visit www.chromosome-screening.org.
Dr. John Park describes the process of Preimplantation Genetic Diagnosis (PGD) and Screening (PGS):
ABC News Video: “PGD at Carolina Conceptions”:
Genesis Genetics talks about the process of PGS