What is non-invasive genetic testing?
If you’re an expectant parent, first of all, congratulations! Your journey to becoming a mom or dad has begun. You’re probably in the early stages of pregnancy, and you’re getting so much information and adding so much to your pregnancy to-do list that your head is spinning. Keep calm and read on. We’ll do our best to make it clearer and less confusing.
The NIPT/NIPS test (Noninvasive Prenatal Testing, or Noninvasive Prenatal Screening) is an elective blood test (and a type of prenatal genetic testing) designed to screen for the most common chromosomal defects in fetuses, including Down Syndrome (Trisomy 21), Trisomy 13 (Patau Syndrome), Trisomy 18 (Edwards Syndrome), and other abnormalities, as well as conditions caused by missing or extra X and Y chromosomes. It can be performed as early as 9+ weeks into the pregnancy.
Who is it for?
Many OB/GYNs are now offering the NIPT or NIPS screening test to all pregnant women, regardless of age or pregnancy risk. That’s because it cannot harm you and poses no threat to your baby (there’s the non-invasive part), as it is just a quick stick of a needle to the mother’s arm. And it can offer a great deal of helpful information, including revealing the baby’s sex in the first trimester, earlier than any ultrasound could determine it. Of course, if you prefer to keep it a surprise, you can let your doctor know not to include that information in your results.
It is important to understand that the NIPT/NIPS test can screen for certain disorders, but it cannot diagnose them, nor can it rule them out. It can’t tell you that your child absolutely will or absolutely won’t have a genetic abnormality. But it can predict the risk fairly accurately.
Who needs this type of genetic screening? Pregnant women who are 35 or older, who have had a child or family member with a chromosomal disorder, or who have had a concerning ultrasound that may have indicated a potential problem with their fetus. Many parents-to-be choose the NIPT/NIPS over amniocentesis or the CVS (chorionic villus) test, because the NIPT/NIPS is a non-invasive form of genetic testing, while amniocentesis and CVS do carry a risk of inducing miscarriage. Although the risk is low, anyone who does not wish to take that slight chance can still get a lot of information from non-invasive testing.
How does it work?
The NIPT/NIPS starts with a simple blood draw from the mother’s arm. Not much more than a slight pinch at worst! The blood is then examined.
Throughout pregnancy, the mother’s bloodstream contains cfDNA which is a mix of her cells and placental cells. Where does it come from? In the uterus, the placenta is the bodily tissue that links the fetal blood supply with the mother’s blood. These placental cells are continuously shed into the mother’s bloodstream. Cell-free DNA (cfDNA) are tiny bits of DNA that have traveled from the placenta into the blood. When these cells die and disintegrate, some of that DNA is released into the bloodstream. Because placental cell DNA is normally identical to the DNA of the fetus, an analysis of cfDNA allows early detection of some genetic abnormalities without any risk of harm to the developing fetus. Since NIPT/NIPS screens both fetal and maternal cfDNA, a genetic condition in the mother may also show up in the results.
To be able to identify chromosomal abnormalities in the fetus, a sufficient percentage of fetal cfDNA (above 4%) must be present in the mother’s bloodstream. This proportion is known as the fetal fraction. This fetal fraction of 4%+ is typically present around the tenth week of pregnancy, hence the timing for the test. When fetal fractions are too low, the test may not work or provide a false negative result. This can happen when testing occurs too early in pregnancy, or when there are sampling errors, maternal obesity, or fetal abnormality.
A positive screening result from the NIPT/NIPS indicates that further testing should be performed: diagnostic testing, to diagnose a disease or disorder.
In addition to the chromosomal disorders that cause the more common genetic syndromes, NIPT/NIPS may now include screening for further genetic disorders caused by missing or unnecessarily repeated sections of a chromosome, and it is beginning to be used to test for changes in single genes that can cause other disorders. Cost is expected to decrease as technology advances, and researchers expect this type of screening to become available for many more uses.
If you are pregnant, or with a partner who is pregnant, and there is a family history of chromosomal disease abnormalities or similar disorders, first and foremost, speak to your doctor. They will help you understand if you may need non-invasive genetic testing to evaluate for genetic disorders. Your doctor may also suggest genetic counseling, especially if they also identify other risk factors in you or your family members.
A genetic counselor will be able to discuss your test results with you within the context of a possible rare disease diagnosis and can recommend the best options for further investigation and genetic testing, if relevant.
