For a couple who wish to have a child or for a woman who is already pregnant, genetics can be used to assess or identify the risks of certain genetic conditions. Here we present to you two test options belonging to precision medicine that can be used during pregnancy planning.
Last June, we presented the usefulness of this type of genetic screening and answered some frequently asked questions. Numerous recent studies show that the rate of carriers of genetic disease is higher than initially envisaged. Two parents who are carriers of the same disease have a 25% chance of transmitting these genetic changes to their children, who will then be affected by the disease in question. It is now possible to offer targeted screening, when a disease is already known in the family, or even extended screening (which may include more than 300 genes), whatever your family history, to allow you to plan a complete pregnancy.
- A “negative” extensive screening result does not completely eliminate the risk of being a carrier. There is in fact a residual risk for each of the genes tested.
- For some genetic diseases, the severity of the disease can vary widely, ranging from mild to severe. Sometimes the severity can be assessed based on the genetic variant identified.
The Non-Invasive Prenatal Screening (NIPS)
By taking a blood sample from the pregnant woman, like at Prenato, it is possible to analyze fetal DNA of cells from the placenta that are circulating in maternal blood and to determine the risk of certain trisomies (21, 13 and 18) and abnormalities of the sex chromosomes of the fetus. The NIPS can be done earlier in pregnancy from the10th week.
This type of test has been available for more than 5 years and is now carried out regularly. Moreover, in August, the American Association of Obstetricians and Gynecologists (ACOG) published new guidelines specifying that the option of NIPS should be offered to all pregnant women, regardless of their age.
- This test is extremely sensitive but still remains a screening test, that is to say that a “positive” result (high risk of Down’s syndrome) must be confirmed by a diagnostic test, such as amniocentesis;
- A “negative” result does not entirely eliminate the risk of a fetal trisomy;
- DPNI cannot detect certain types of chromosome abnormalities, birth defects, or genetic diseases.
Genetic Counselling in Preconception and Perinatal Care
The reasons for being tested or not being tested are numerous and differ from one person to another. For some, it is important to know whether a disease can be prevented or treated if a positive result is found. In some cases, there is no treatment, but the test results can help a person make decisions when planning for pregnancy. In addition, a genetic test result can affect other family members of the person being tested. A genetic counselling meeting offers couples support to make informed decisions and to better understand their results and the possible consequences on their lives.
- Before getting a test, a genetic counselor can discuss with you the pros and cons of testing, the types of results you can get, the consequences of those results for you and your family members, and the options available;
- When the results are available, the genetic counselor will inform you of these results, the residual risks, the risks of your child being affected, the disease itself, the treatment options (if available), your reproductive options and the resources available to you.
A genetic counselor takes all important factors, such as your family and personal history, into account, and discusses with you the next steps after you get your genetic test results. Its support allows you to assess all the risk factors and obtain answers to your questions. It can help you avoid a false sense of security or avoid anxiety based on your test results.
Nathalie Bolduc, MSc, CGAC, CGC
Certified genetic counselor