Preimplantation Genetic Testing (PGT/PGS)
Preimplantation Genetic Diagnosis
Have you thought about genetic testing? Prospective parents have been able to get genetic testing for themselves for a long time, but carrying a recessive gene does not mean you will pass it on to your child. Some conditions arise spontaneously, too, and testing the parents will not reveal any risk of some genetic problems.
Today, it’s possible to test an unborn baby for many conditions. However, people who have struggled to conceive would prefer not to wait until they are pregnant to learn that their child might have a genetic condition.
Preimplantation Genetic Testing (PGT)
Preimplantation genetic testing (PGT) is an umbrella term that covers preimplantation genetic diagnosis, and chromosome and genetic screening. Preimplantation genetic testing is carried out on an embryo conceived by IVF before the embryo is transferred to the uterus. PGT examines a few cells removed from the part of the embryo that will develop into the pre-placenta (the trophectoderm) and does not touch the inner mass cells that will develop into the baby.
Only embryos that have a genetic chance of developing into a healthy baby will be transferred.
Preimplantation genetic diagnosis (PGD)
Monogenic genetic testing (PGT-M), formerly called PGD, can determine if the embryo is carrying genes for one of the specific genetic diseases[KT1] s known to be caused by a mutation in one gene. The test can determine if the child is carrying the gene and will be affected by the condition, whether the embryo does not have gene and therefore will not have the condition, or whether the embryo is carrying a recessive copy of the gene (as was the parent) and will not him or herself be affected by that gene, just as the parent has been unaffected.
Monogenetic testing is used to look for conditions like cystic fibrosis, Huntington’s, sickle cell anemia, fragile-X syndrome, and Tay-Sachs. It can also be used to examine embryos for sex-linked conditions, which are passed through the mother and only affect boys who inherit their mother’s X gene, such as hemophilia and most of the muscular dystrophies.
Preimplantation genetic screening
Preimplantation genetic testing can look for aneuploidy (PGT-A), which is an incorrect number of chromosomes. (This test was formerly called preimplantation genetic screening, or PGS.) Aneuploidy is a major cause of miscarriage or failed implantation because many of these abnormalities are not compatible with life. Down’s syndrome (trisomy 21) is the most well-known of the survivable chromosomal abnormalities. Chromosomal abnormalities can come from either eggs or sperm; both parents have some eggs or sperm that carry abnormalities.
PGT can also be used to look for structural rearrangement (SR) in chromosomes, which can be a cause of recurrent miscarriage. Parents with a known structural rearrangement are more likely to produce embryos with chromosomal abnormalities. This test is known as PGT-SR.
Next-generation sequencing and mosaicism
Unfortunately, some embryos have a condition called mosaicism, where not all of their cells are genetically identical. Because PGD looks at only a few cells, the test may either miss a genetic disorder present in an untested cell or find a genetic disorder in a few cells. Next-generation sequencing is now able to determine the percentage of cells affected by mosaicism, allowing the physicians and patients to make a more informed decision about transferring an embryo.
Risks of PGD and PGS
It is possible that an embryo may have a genetic condition that is not identified during testing. Testing should be confirmed by prenatal testing at the appropriate time during the pregnancy.
It is also possible that all embryos in each IVF cycle will be found to have some genetic disorder, leaving no healthy embryos for transfer to the uterus. This risk is higher for older parents, because both sperm and eggs show higher rates of chromosome abnormality as parental age increases.
Cost of preimplantation genetic testing
Preimplantation genetic testing can add between $4000 to $7000 to the cost of an IVF cycle. The costs are due to the sampling required and for genetic testing.
Who should use PGD?
PGD, or PGT-M, is recommended for anyone who is a known carrier of a gene that leads to a condition you do not want to give to a child. PGS, or PGT-A and/or PGT-SR, is suggested for women who have a history of miscarriage, who are older, or who simply have personal reasons for testing.
In any case, parents should work with a genetic counselor who can help them understand the specific decisions and outcomes they may face as a result of testing.
Appointments are Available at Our Raleigh, NC Fertility Clinic
Let’s evaluate and explore your options together. Atlantic Reproductive is a premier source of fertility treatment and testing in the Triangle. Our practice sees patients from Raleigh, Durham, Cary, Chapel Hill, Fayetteville and beyond. Contact Dr. David Walmer and Dr. Susannah Copland today and let our team assist you in building your family!