PGT is only possible when you’re electing to have a baby using in vitro fertilization.
OVER THE PAST DECADE, there’s been a profound increase in the number of genetic tests available to consumers. Direct marketing and testimonials by public figures and celebrities have increased awareness as well as our desire for these tests. Through consumer sites such as My Heritage, Living DNA and 23andMe, we can now explore our ancestry, find out why raw broccoli and brussels sprouts taste bitter to us and test for the hereditary cancer-associated genetic variants in the BRCA genes.
This genomic revolution has spread to human reproduction, as well, with preimplantation genetic testing, or PGT. This refers to testing embryos before they’re implanted inside the mother’s womb.
American model and cookbook author Chrissy Teigen proudly shared her choice to do preimplantation genetic testing for aneuploidy, or PGT-A, while undergoing in vitro fertilization. With PGT-A, a complete chromosomal analysis of each embryo is conducted. The purpose of PGT-A is to select the embryos with the highest implantation potential and reduce the emotional and physical trauma from a pregnancy loss or termination. PGT-A also helps transfer embryos one by one, and decreases the complications related to multiple births. It’s estimated that PGT-A is currently performed in 40 percent of all IVF cycles in the U.S.
PGT is only possible when you’re electing to have a baby using IVF. The process begins by stimulating the ovaries with daily injections of follicle-stimulating hormones for 10 to 14 days in order to produce more mature eggs. The eggs are harvested and put together with the sperm in the embryology laboratory, and the resulting embryos are cultured for five to six days. A biopsy of five to 10 cells is obtained from each embryo and sent to a genetic testing laboratory for comprehensive chromosome analysis before being frozen. Once the results are in, the selected embryo is thawed and implanted with the hope of a happy and healthy baby.
Genomes are our genetic blueprint, the complete set of genes present in a cell. In every cell in our body, we have 23 pairs of chromosomes.  Aneuploidy is an imbalance in the chromosomal number in a cell due to one missing or additional chromosome. An aneuploidy that many people are familiar with is Down syndrome, where the individual is born with three copies of chromosome 21. An embryo with a chromosomal imbalance will stop developing, result in miscarriage or present with major birth defects. Aneuploidy is the most common cause of IVF failure and miscarriage.
PGT-M is the recommended test for couples who are at risk for inheriting a single gene mutation. The M stands for monogenic, meaning a disease resulting from a mutation in a single gene, and this test can effectively identify the embryos that are affected with a specific inheritable condition. Basically, if we know the mutation, we can test the embryos. Hundreds of inheritable conditions, many of which result in a short life expectancy or with limited treatment options, can be identified with PGT-M. A couple in our Miami practice has a 3-year old son born with a genetic disease, resulting in early brain damage. Their hope was to avoid the same genetic abnormality in future children with PGT-M. A test was developed for their specific familial mutation before the IVF cycle began, and the happy parents recently celebrated the birth of a baby girl.
PGT-M can be also performed for hereditary cancer genes. The National   Comprehensive Cancer Network recommends discussion of the reproductive options – including PGT-M – for couples in which at least one member carries a BRCA gene mutation. I recently performed an egg retrieval on a 24-year-old young woman who tested positive for the BRCA2 mutation. She underwent genetic testing following the breast cancer diagnosis of her 27-year-old sister. Though not currently in a relationship, she electively chose to freeze her eggs and select embryos without mutation for the future.
In addition to PGT-A and PGT-M, there are two variations of PGT: PGT-HLA for matching for tissue donation and PGT- SR for translocations. PGT-A automatically determines the sex of the embryo. However, traits controlled by multiples genes and environmental factors such as height, intelligence and birth defects or newly acquired mutations cannot be tested at this point in time with PGT.
I’m excited about the rapidly growing advancements in the field of preimplantation genetic testing. Recent studies indicate how embryos shed their DNA into the media in which they are growing, and significant improvements in testing for aneuploidy from the media have been reported. Hopefully, in a few years, we may no longer need to biopsy embryos to perform preimplantation genetic testing, and PGT-A can be a routine part of all IVF cycles. I’m a firm believer in the positive power of PGT. I’ve seen patients become parents for the first time, while others add healthy babies to their families; it’s inspiring and gratifying.
Awareness of the availability of preimplantation genetic testing, as well as the purpose behind the testing, is essential. Our ultimate goal should be to use this scientific advancement to alleviate human suffering, decrease pregnancy loss and terminations, reduce pregnancy complications and help individuals create or grow their family.
With these powerfully positive purposes in mind, we can promote preimplantation genetic testing for the greater good.
By Sinem Karipcin M.D.
https://health.usnews.com