Decades ago, parents-to-be with a family history of genetic illness or hereditary cancer were often faced with the difficult decision of either never having children or potentially passing along the disease. Today, there are many types of genetic tests, including preimplantation genetic testing (PGT) and chorionic villus sampling (CVS), a form of prenatal testing, which allow prospective parents to take charge of their future child’s health proactively.
Here, we’ll explain how all these tests fit together and how to discern which tests, if any, are right for you.
Genetic Screening and Testing Before Pregnancy
According to the National Institute of Health, genetic testing includes different screening and diagnostic tests that work in concert prior to and during pregnancy to maximize the odds of having a healthy child by screening for single gene disorders and chromosomal abnormalities.
Traditionally, genetic carrier screening has been offered to patients based on their family history or ethnic background. Individuals deemed to be at higher-risk of being a carrier were screened for a limited number of mutations that account for the majority of the disease in question. The American College of Obstetrics and Gynecologists recommends that carrier screening for certain diseases be offered to all women, preferably before they become pregnant, regardless of their family history or ethnic background.
There is also a growing trend among fertility specialists and OB/GYNs to offer expanded carrier screening, according to the ACOG. This test screens for thousands of rare genetic conditions to see if you’re a carrier, so you know the potential health risks to offspring and your options for prevention before pregnancy.
In vitro fertilization (IVF) paired with PGT can help offer peace of mind to couples who are known carriers of a single gene disorder, such as cystic fibrosis or Tay-Sachs, and to women of advanced maternal age concerned about an increased frequency of missing or extra chromosomes in their eggs (as in the case of Down syndrome).
PGT for single gene disorders (PGT-M) identifies familial genetic disease while PGT for aneuploidy (PGT-A) identifies which embryos have the greatest risk for a chromosome abnormality. Only chromosomally normal embryos that show that they are not affected by the familial genetic disease are transferred to the uterus, thereby significantly decreasing the likelihood that the pregnancy will result in a child with the condition.
Genetic Screening and Testing During Pregnancy
Although PGT is highly accurate, no test comes without the risk of error. To confirm the results of PGT, the ACOG recommends prenatal testing, such as CVS, which samples tissue taken from the placenta, or amniocentesis, which samples the amniotic fluid surrounding the developing fetus. CVS and amniocentesis are offered to women that have an indication of a pregnancy at-risk for certain genetic abnormalities, whether or not they elect to undergo PGT. Both tests carry a small chance of miscarriage.
For people in higher-risk categories, such as advanced maternal age or family history of genetic illness, CVS is considered advantageous over amniocentesis because it can be performed as early as ten weeks into the pregnancy, and the test results come back faster, ACOG notes.
Empowering Prospective Parents
While both PGT and prenatal testing can confirm the presence of a genetic condition, PGT is the only available test that determines the health of embryos before implantation. By preventing hereditary illness at the embryonic level, you can reduce the risk of discovering that a pregnancy is affected by hereditary illness and help avoid the emotional distress of deciding whether to continue the pregnancy or have a child affected by the condition. The decision to undergo any sort of genetic testing is a deeply personal one, and you should consider the outcomes carefully, which can include consulting with a genetic counselor.
Today, the wealth of genetic tests available to help parents-to-be plan for the health of their future children is unparalleled. By understanding your options at the different stages, you can decide what steps to take to plan for your family’s future.
Dawn Michelle Lipscomb, PhD, is a biophysicist, podcast host, and science writer. While finishing a dual B.S. in Physics and Biology at UT San Antonio, she published research on planetary biosignatures for space exploration at NASA-JPL and designed THz bioeffects experiments for human tissues at the Air Force Research Laboratory. In 2017, she completed her Biophysics doctorate at UC Berkeley by developing a new method for imaging proteins that regulate gene expression using cryo-electron microscopy. Today, she co-hosts a live video podcast series on regenerative medicine and writes articles about groundbreaking research in aging and genetics.