Preimplantation Genetic Testing (PGT)

Selecting the healthiest embryo for embryo transfer day is an important skill that increases a patient’s chances for a baby.

Preimplantation Genetic Testing – Aneuploidy (PGTa) (formerly known as Preimplantation Genetic Screening/PGS) has dramatically increased the live birth rates of children born as a result of IVF.

These techniques help your IVF team to analyze and understand the health of your embryo prior to transfer into the uterus. They have saved countless couples the heartache of inevitable miscarriage, as well future investments in frozen embryo storage and FET (frozen embryo transfer) IVF cycles likely destined for failure. Making an informed decision about transferring ONE healthy embryo has also helped couples decrease the risks for multiples.

Genetic screening of embryos is performed on the healthier embryos after they have developed for 5 or 6 days in the laboratory. A few cells are removed from each embryo and sent to a genetics lab to analyze the chromosomes and make sure they are all present in the right amounts. An embryo has an abnormal number of chromosomes may fail to implant in the uterus or may result in a miscarriage, or result in a baby with a genetic syndrome such as Down syndrome or Turner syndrome.

Aneuploidy is the term used to describe the condition where an abnormal number of chromosomes are present. Aneuploidy occurs in all age groups, but the proportion of aneuploid embryos is significantly higher in women ages 35 and older.

After results on the testing are available, the chance of pregnancy with a genetically normal embryo is excellent, with a dramatically reduced risk of miscarriage. The transfer of a single embryo is the routine. Only in rare circumstances would it be necessary to transfer 2 embryos after genetic screening.

Genetic prenatal carrier screening can also be performed to determine if you or your partner carry a recessive mutation (e.g. cystic fibrosis, sickle cell disease) which could be passed on to a child.  If both the egg and sperm carry the same mutation, patients can pursue additional embryo genetic testing, PGT-mutation (PGT-m) to avoid passing on the disease to your children.

For those patients who choose not to undergo additional genetic or embryonic testing, our team can still make expert decisions about which of your embryos are of the highest quality and will have the greatest potential for implantation.

Preconception genetic carrier screening is offered to patients before becoming pregnant to determine the chances of having a child with a genetic disorder. Many people are carriers of genetic mutations, but have no signs or symptoms of the disorder because a carrier still has one normal gene in addition to the abnormal, mutated gene.  You may be a carrier for a serious genetic disease (such as cystic fibrosis), but never know without genetic screening.

If two people carry the same genetic mutation and have a child together, there is a high risk that they will have a child with a genetic disorder. The majority of children born with a genetic condition have no family history of that disease because carriers are typically unaware that they have a genetic mutation.

If both parents are carriers, there is a 25% chance that the child will get the abnormal gene from each parent and will have the disorder. There is a 50% chance that the child will be a carrier of the disorder—just like the carrier parent. There is a 25% chance that the child will only inherit the normal genes. If only one parent is a carrier, there is a 50% chance that the child will be a carrier of the disorder and a 0% chance that the child will have the disorder.

Preimplantation Genetic Testing – Mutation (PGT-M) can be performed to test the embryo of a couple who are both carriers of the same disease.  This allows us to identify which embryos would result in a child born with the disorder.  We can also identify the healthy embryos without the disease to put back in a woman’s uterus for her to have a child without the disease.  More on PGT-M below.

People are at increased risk of being a carrier of a genetic mutation if they already have a child with a genetic disorder, if there is a family history of a genetic disorder, or if they belong to a certain ethnic group that has a high rate of certain genetic disorders.

Ethnic groups with an increased risk of genetic disorders include:

• Non-Hispanic white individuals should be offered cystic fibrosis carrier screening.
• People of Eastern European Jewish descent (Ashkenazi Jews) should be offered screening for Tay–Sachs disease, Canavan disease, familial dysautonomia, and cystic fibrosis. Individuals can ask about screening for other disorders. Carrier screening is available for mucolipidosis IV, Niemann–Pick disease type A, Fanconi anemia group C, Bloom syndrome, and Gaucher disease.
• People of African, Mediterranean and Southeast Asian heritage should be offered screening for thalassemias and sickle cell disease.

Though targeted genetic screening can be performed, many resources, such as NxGen, now offer carrier screening for up to 120 genetic disorders that can affect your pregnancy, the health of your baby, and your family’s future in one simple test. These tests can be viewed as a way to provide a couple with the most information before they start treatment or add to their family.

In addition to the genetic screening, patients will receive genetic counseling to discuss the results.  If a patient and partner learn that they are both carriers of a genetic mutation, there are several options:

• They can proceed with becoming pregnant, then undergo prenatal diagnosis with amniocentesis or chorionic villus sampling to see if the baby is affected.
• They could also undergo in vitro fertilization with preimplantation genetic testing – mutation (M) to identify the affected embryos and avoid using those to become pregnant.  NxGen will assist with the costs of such treatment in the event a couple is identified as being carriers of the same mutation.
• Couples also have the option of using donor sperm or donor eggs that do not have the mutation so that their child will not be affected.