GENETIC TESTING
GENETIC TESTING
AFMC offers PGT to increase the chance of chance of a healthy pregnancy. PGT is a procedure in which embryos created during an IVF cycle are tested for genetic abnormalities prior to being transferred to the patient’s uterus. This helps our physicians choose the healthiest embryo for transfer.
CARRIER SCREENING
One of the most common reasons that an embryo transfer does not result in a pregnancy is due to abnormal embryo genetics. Carrier screening is a type of testing used to assess genetic risks to a patient/couple’s offspring that would not be evident just from personal or family history alone. The genetic conditions we look for through carrier screening are called recessive disorders, where both copies of the gene have to be no longer working properly in order for an individual to actually show symptoms of that condition.
GENETIC CONDITIONS
In some cases, both members of a couple may be carriers for a recessive genetic condition such as cystic fibrosis or sickle cell anemia.
Carrier screening also typically looks for common X-linked conditions, which are conditions that only females (individuals with two X chromosomes) carry such as Fragile X syndrome. It is completely normal to be a carrier; most people carry one or more recessive conditions and are asymptomatic. However, if a carrier has a child with someone who also carries the same condition, then there is a significant risk (25%) of having a child with that genetic disease.
PGT TESTING
If both members of a couple are found to be carriers of the same disease, or a female carrier for an X-linked disease, it is possible through in vitro fertilization (IVF) to screen embryos via pre-implantation genetic testing (PGT) and determine before pregnancy is attempted whether or not each embryo is predicted to be affected with the genetic disorder. Only embryos that are not affected with the condition are transferred back into the uterus to attempt pregnancy.
ASSESSMENT
Even if a couple elects to undergo IVF without PGT, there are a few helpful considerations such as being aware that additional prenatal testing is indicated. In some cases, preparing a special pediatric care team to be ready after birth. Carrier screening is used to assess genetic risks that would not be evident from personal or family history alone. Carrier screenings look for recessive disorders, where both copies of the gene are no longer working properly in order for an individual to actually show symptoms of that condition.
IVF WITH PGT PROCESS:
- Blastocyst Development
- Biopsy
- Testing
- Review
During an IVF cycle, eggs are retrieved from the female patient and fertilized with sperm in the IVF laboratory. The embryos created are allowed to develop for 5-7 days until they reach the blastocyst stage of development.
The embryologist takes a small sample of cells from the outer layer of the blastocyst. This outer layer will later develop into the placenta and other supporting structures of the pregnancy.
- The embryos are biopsied and frozen within our IVF laboratory where they are safely stored. Meanwhile, the biopsied samples are sent to an outside laboratory that specializes in PGT.
PGT testing takes 1-2 weeks for the results to come back. Your doctor will review the results with you to help choose which embryo to use for transfer. Some embryos are then chosen for a frozen embryo transfer cycle to be scheduled at a later time.
AFMC OFFERS TWO TYPES OF PGT:
PGT-Aneuploidy (PGT-A)
Most people have 46 chromosomes because they inherit 23 chromosomes from each parent. If an embryo or a cell is missing a chromosome or has an extra one, it is called aneuploidy. Monosomy is a missing chromosome and trisomy is an extra chromosome.
A child can only survive one type of monosomy, Turner syndrome, which is the absence of one of the X chromosomes. Trisomy of chromosome pairs can sometimes result in live birth, Down syndrome, also called trisomy 21 (an extra chromosome in normal pair # 21), Turner syndrome (trisomy 18) and Patau syndrome (trisomy 13). Down syndrome affects 1 in 700 babies, according to the Centers for Disease Control and Prevention.
Aneuploidy is one of the greatest causes of failed implantation for pregnancy and miscarriage, as well as a major cause of birth defects in children.
PGT-Monogenic Conditions (PGT-M)
Preparing for PGT-M typically requires several months before a PGT lab is ready to analyze samples. This is because PGT-M involves the creation of a custom test for the family (sometimes referred to as a “probe”) that is tailored to the specific genetic variants(s) involved and other identifying genetic markers. PGT-A can be completed concurrently with PGT-M if desired by the patient or advised by a doctor. Performing PGT-M prior to embryo transfer can greatly reduce the risk of having a child with a specific genetic disorder.
Limitations of PGT
Furthermore, there are some rare types of chromosome abnormalities that may not be detectable by PGT-A or PGT-SR. In addition, PGT-M can only detect the specific condition(s) being targeted. As such, your doctor may suggest prenatal genetic testing as a follow-up. Further discussion of prenatal testing options with a prenatal genetic counselor and/or obstetrician is recommended. In addition, PGT is unable to screen for disorders that are without an identifiable genetic cause (e.g. spontaneous birth defects, most cases of cerebral palsy, or autism, etc.) for which all pregnancies are at risk, regardless of how they are conceived.
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