Preimplantation Genetic Testing (PGT) and screening are two different methods doctors use to identify genetic abnormalities in embryos. PGT is useful in identifying genetic diseases and chromosomal abnormalities prior to embryo transfer in an IVF cycle. Screenings are done before conception, during pregnancy or immediately after birth. Here we offer a breakdown of the different screening and preimplantation testing methods and what they can uncover.
What Are Genetic Diseases?
Genetic diseases and disorders are conditions caused by a harmful change (mutation) to a gene. This change affects your genetic makeup, though just because you or your partner test positive for the mutation doesn’t mean you have or will develop the disease.
Genes are made of DNA, which is essentially an instruction manual for your cells and how they function. You receive half of your genes from your mom and half from your dad in the form of chromosomes. These genes determine your features, which is why you may have your mom’s brown eyes and your dad’s long legs.
When a baby inherits a mutation from one or both parents they are at risk for a genetic disorder. This disorder may be present at birth in the form of a birth defect or it may develop over time. There are three specific types of genetic disorders. They are:
- Chromosomal: Your chromosomes are structures within each cell that contain DNA. Chromosomal genetic disorders arise from missing, disordered or duplicated chromosomes.
- Complex: YAlso called multifactorial, these disorders arise from a combination of gene mutations and other factors. For example, damaged DNA combined with chemical exposure increases a risk for a genetic disease. Some other factors include lifestyle (eg. diet, alcohol, tobacco or drugs) or certain medications prescribed by your doctor.
- Single-Gene: Single gene or monogenic conditions happen when a single gene has a mutation.
Types of Screening for Genetic Diseases
If you and your partner know of a family history of certain genetic diseases prior to getting pregnant or beginning an IVF cycle, your doctor will likely recommend genetic counseling. You’ll meet with a trained counselor who, through a series of questions, will determine your risk for passing on a genetic disease. If there is a risk, you’ll be referred for additional testing.
The initial test is called a carrier screening. Through a sample of your and your partner’s blood or saliva, your DNA will be assessed for genetic mutations of specific diseases even if you or your partner don’t actually have the disease. This screening determines if both you and your partner carry a genetic predisposition for a disease and the likelihood of passing it on. In the case of recessive genetic diseases, like Cystic fibrosis, both you and your partner need to be carriers of the gene.
Prenatal screening is conducted during pregnancy. The doctor takes blood from the mother and, along with ultrasounds, assesses the risk for specific genetic conditions such as Down’s syndrome and neural tube defects in the developing fetus.
In addition to the conditions mentioned above, carrier and prenatal other disorders uncovered through carrier screening and prenatal screening include:
- Fragile X Syndrome
- Spinal Muscular Atrophy
- PKT (Phenylketonuria)
- Edwards Syndrome (trisomy 18)
Newborn screening tests for several conditions before symptoms show up in the baby. The benefit of newborn screening is that the doctors can begin treatment as early as possible and prevent serious and life-threatening complications.
Preimplantation Genetic Testing (PGT)
PGT tests for certain genetic diseases and chromosomal abnormalities of an embryo as part of an IVF cycle. Prior to implantation, cells removed from pre-placenta cells – not cells that grow into a fetus – are tested. The removal and testing of those cells, described below, in no way harms the embryo or interferes with its development.
This type of PGT assesses the embryo for aneuploidies that indicate a chromosomal abnormality. A chromosomal abnormality occurs when there are missing or additional chromosomes. When there is a chromosomal abnormality, the embryo is at risk conditions like trisomy or Down syndrome, as well as many others. This can result in developmental birth defects, miscarriage or stillbirth.
PGT-M tests for monogenic disorders that occur when one or both parents have a known genetic disease. The embryos are assessed for certain genetic mutations associated with the disease, allowing you to choose to implant only those embryos that show no evidence of the genetic mutation. Some examples of these genetic diseases are:
- Cystic Fibrosis
- Sickle-Cell Disease
- Huntington’s Disease
- BRCA Mutations
- Spinal Muscular Atrophy
The SR stands for structural rearrangement and that’s exactly what this form of PGT looks for. If both parents test positive for a structural rearrangement, the odds for the pregnancy to result in a live and healthy birth are low. Conditions associated with SR are typically complex and affect the major organs. Also structural rearrangement is often related to multiple miscarriages.
HALO Can Help
Of course the specific genetic diseases for which you are screened depend on your and your partner’s knowledge of your family history and possible presence of a genetic condition. Testing is entirely up to those involved and it is a highly personal decision.
If you need additional information or would like to meet with a genetic counselor, please contact Halo Fertility. Together we’ll find a way to realize your dream of growing your family.