Genetic Testing and Diagnosis
Preimplantation Genetic Testing for Monogenic Disease (PGT-M)
While preimplantation genetic testing for Monogenic Disease (PGT-M) is not necessary or even advised for everyone, it is an invaluable technology for those who may be carriers of or affected with a specific genetic disease, as it can greatly increase the chance of having offspring without that disease. For those interested in such testing, a meeting with a genetic counselor is required and pre-IVF set up can take weeks to months as PGT-M is highly customized for each family.
Those who choose to have embryos tested must undergo IVF (in vitro fertilization), in order to produce embryos to test. In IVF, the female receives fertility medications, which stimulate her ovaries to mature multiple eggs. Eggs are removed and fertilized with the male sperm in our laboratory and early embryos (blastocysts) begin to form. Learn more about IVF.
Ideally, the couple undergoing IVF will produce multiple embryos. At day 5 to 7 of embryonic development, a small sample of cells is removed (biopsied) from each embryo and sent to a highly specialized PGT laboratory, where it is tested for the familial mutations. The biopsy process does not appear harm the embryos, according to some published research and our experience. After testing, embryos determined to be free of genetic disease may be transferred into the woman's uterus. Because the testing process takes about a week, embryos need to be frozen. In this event, a frozen embryo transfer cycle is arranged once PGT-M results are known.
When is PGT-M recommended?
PGT-M is recommended only for those individuals or couples who have or carry a specific genetic disease and are thus at risk for passing this condition on to their child.
There are various ways to determine that a male or female partner may carry a genetic condition: a couple may have previously given birth to a child with a genetic disease; a family member(s) may carry a genetic mutation; or a condition may be found during routine, pre-treatment genetic carrier screening. At PFC, we offer expanded carrier screening of 200+ conditions to all couples pursuing treatment in hopes of identifying those who might benefit from PGT-M. Once a genetic mutation (or variant) has been identified, the next step is to work with our genetic counselor to determine whether PGT-M is possible for that genetic condition and what would be required for PGT-M test set up.
Additional Genetic Testing During Pregnancy
The accuracy of PGT-M is generally between 95% and 99%. Additional genetic testing during pregnancy, as described below, is recommended to confirm the PGT-M results.
The procedures available to test for chromosome abnormalities and other specific genetic conditions during pregnancy include amniocentesis and CVS(chorionic villus sampling).
Amniocentesis may be conducted between 16-20 weeks of pregnancy. For this procedure, a fine needle is inserted through the woman's abdomen and guided into a pocket of amniotic fluid within the uterine cavity with the aid of ultrasound imaging. A small sample of amniotic fluid is taken, which contains sloughed off cells from the growing fetus, and these can be used for genetic testing.
CVS (chorionic villus sampling)
This procedure may be conducted earlier than amniocentesis, between 10-12 weeks of pregnancy. Here, doctors remove a tiny sample of the placenta via a small needle inserted into the abdomen or a small tube inserted through the cervix. As with amniotic fluid, this tissue sample can be used for genetic testing. Because the results of amniocentesis and CVS are available fairly early in pregnancy, there is typically enough time to make any decisions about whether to continue a pregnancy if a problem is identified.
Disorders for which PGT-M is offered
PGD is capable of analyzing the majority of genetic diseases and is an accessible technology for most patients. If you think PGT-M might be appropriate for you, an appointment with a PFC genetic counselor can be coordinated.
Preimplantation Genetic Testing for Aneuploidy (PGT-A)
Those undergoing IVF may also have embryos tested through a process called preimplantation genetic testing for aneuploidy (PGT-A). Here, embryos are analyzed for the number of chromosomes each contains. Chromosome count is an important indication of embryo health. Too few or too many chromosomes can lead to a number of issues, such as failure for an embryo to implant, miscarriage, and chromosome abnormalities in a fetus or child, such as Down syndrome, a condition characterized by various significant physical and cognitive difficulties.
When is PGT-A recommended?
PGT-A may be recommended to women who have experienced recurrent miscarriage or repeated unexplained IVF embryo implantation failure. We may also recommend PGT-A to those hoping to become pregnant in their late 30s or 40s, when chromosome abnormalities are more likely to occur. PGT-A can also enable parents to identify the sex of the embryos, as some may wish to transfer embryos of a given sex. Sex selection is often chosen by parents that already have a child or children of the other sex. This is then referred to as "family balancing." We at PFC do not necessarily advocate undergoing IVF solely for sex selection but we do understand that there may be personal reasons for this choice and we do offer it to those who wish to do it. Those who make this decision are advised that they may be eliminating roughly half of their embryos from consideration for transfer, and thus sex selection may diminish their overall chances of achieving a pregnancy from a given cycle.
Those who decide to pursue PGT-A are required to meet with a PFC genetic counselor prior to their cycle. This is so we are able to ensure that they have a complete understanding of the genetic evaluation process and its potential ramifications.