What is Preimplantation Genetic Testing (PGT)?
Preimplantation genetic testing (PGT) is an evaluation that can be performed prior to embryo(s) being transferred during in vitro fertilization (IVF). PGT allows patients and fertility specialists to evaluate and select the healthiest, most viable embryos that are likely to be free of any genetic or chromosomal abnormalities before transfer. This method provides patients with the opportunity to reduce their children’s risk of genetic disease prior to pregnancy.
Types of Preimplantation Genetic Testing (PGT):
There are two primary types of preimplantation genetic testing:
- PGT-A (Preimplantation Genetic Testing for Aneuploidy) is genetic screening of embryos for chromosomal abnormalities. It involves biopsy of embryos reaching the blastocyst stage during In Vitro Fertilization (IVF) to determine which embryos have normal chromosome number and structure.
- PGT-M (Preimplantation Genetic Testing for Monogenic disease) is preimplantation genetic testing of embryos to detect hereditary single gene (monogenic) defects, such as cystic fibrosis (CF). The technique decreases the risk of transmitting hereditary disease to the children. PGT-M requires biopsy of the embryos to select normal or unaffected embryos for transfer during IVF treatment.
Why is preimplantation genetic testing (PGT) important for fertility patients?
Typically, during IVF, one embryo is transferred into the uterus 5-7 days after fertilization at the blastocyst stage. Not all embryos progress to the blastocyst stage and not all blastocysts are genetically normal. Selecting the right embryo for transfer is tricky because looks can be deceiving. The embryo may look good and still be genetically abnormal.
Remarkably, about 40% of chromosomally abnormal embryos can reach the blastocyst stage. Not surprisingly, when a single non-biopsied blastocyst is transferred, the ongoing pregnancy rate in patients under the age of 35 is only about 40%.
How common are genetic disorders?
Chromosome abnormalities (aneuploidy) in human embryos is the major cause of in vitro fertilization (IVF) failure and miscarriage. The incidence of chromosomal abnormalities in embryos increases exponentially in women over the age of 35 years.
Data from embryo biopsy demonstrates that the incidence of genetically abnormal embryos increases from 30% to 50% in patients under 35 years of age to 80% in women 42 years of age or older. This explains why live birth rates per IVF egg-retrieval cycle decrease from 55% in young patients (under 35) to about 15% in women aged 41–42 years.
How is Preimplantation Genetic Testing (PGT-A or PGT-M) performed?
Embryo biopsy utilizes sophisticated microscopic laser technology to remove 5-15 cells from the trophectoderm layer of the embryo which later in pregnancy becomes the placenta. The cells destined to become the fetus are not disturbed. The cells are then sent to the genetic laboratory for Next-Generation Sequencing (NGS) analysis of the chromosomes to determine if the embryo is genetically normal (PGT-A). The cells can also be tested for hereditary monogenic or single gene defect (PGT-M).
Benefits of PGT
- An embryo biopsy can help detect chromosomal or genetic abnormality.
- Performing an embryo biopsy can help reduce multiple pregnancy rates by providing the insight needed to select a single healthy embryo for transfer.
- An embryo biopsy can decrease risk to couples or individuals with serious inherited genetic disorder from transmitting it to their children.
Should PGT always be performed?
Embryo biopsy is indicated in selected cases such as:
- Known parental chromosome abnormality.
- In cases of parental single gene defect, such as cystic fibrosis, sickle cell disease or spinal muscular atrophy. to minimize the risk of transmission of serious hereditary disease to the children.
- Recurrent pregnancy loss due to abnormal fetal chromosomes.
- Gender selection or family balancing.
- Strong desire to decrease risk of miscarriages.
What are the challenges and risks of embryo genetic screening?
- False positive results, which may result in the discarding of otherwise healthy genetically normal embryos. At Boca Fertility, we use a platform called Juno Genetics, which has been validated to decrease the risk of false positive results.
- Increased cost and complexity of IVF treatment.
Overall, PGT does not improve the quality of the embryos you have created; however it can shorten your time to pregnancy by helping us select only those with the highest reproductive potential for transfer. It can also reduce your risk of miscarriage and failed transfer cycles, reducing the amount of medication and procedures necessary to get to your goal of a happy, healthy pregnancy.
To learn more about genetic testing at Boca Fertility, please call our office to schedule an appointment. Our fertility specialists will help you decide if genetic testing is the right path for you.