Noninvasive Prenatal Testing (NIPT): How it Works

noninvasive prenatal screening

In the past decade there have been numerous advances in the field of reproductive medicine with cell free DNA (cfDNA) or noninvasive prenatal testing (NIPT) being at the forefront of the advanced DNA testing options available during a pregnancy. The main idea behind this screening test is to test the fragments of DNA that come from the placenta and are present in the mother’s blood. The placenta and the fetus typically originate from the same cells and hence we are indirectly testing the fetus. NIPT can be pursued anytime during the pregnancy after 10 weeks gestational age, with some laboratories offering this test as early as 9 weeks. The results from this test are usually available in 5-7 days but it could take longer.

What Does This Test Look For?

Cell-free DNA testing is routinely used to screen for the most common chromosome conditions associated with chromosome 21 (trisomy 21 or Down syndrome), chromosome 18 (trisomy 18), chromosome 13 (trisomy 13), and the sex chromosomes (that determine the gender of the fetus). Screening for other chromosomal aneuploidies as well as screening for chromosomal microdeletions and microduplications (smaller pieces of chromosomes missing or extra) through cell-free DNA testing is also available. In the past few years, some laboratories have developed this technology to screen for single gene disorders as well.

What kind of Results Can I Expect From This Test?

Cell free DNA testing is a screening test. Based on the screening results, a patient will fall into a high or low risk category for the conditions screened for – the test does not provide a definite yes or no as to whether the fetus has the condition that is being screened for. Low risk typically indicates a risk much less than 1 in 1000 (0.1%) for the fetus to be affected with the condition.

The sensitivity (accuracy of testing) of this test may vary from one condition to another that this test screens for. Most labs offer a sensitivity of around 99.99% for the most common chromosome aneuploidies discussed above. It is important to remember that a low risk cell-free DNA screen does not eliminate all genetic risks associated with a pregnancy. Also, there is a baseline risk for birth defects (approximately 3 to 4%) despite screening negative.

If a patient screens high risk on a cell free DNA test, further testing with the help of a diagnostic test such as a chorionic villus sampling or an amniocentesis should be considered to confirm this result. Irreversible decisions should not be made solely based on a cell-free DNA test.

There is also the possibility of a NIPT test failure or an inconclusive result due to many reasons including laboratory failure, inappropriate sample collection or transportation, low amount of fetal DNA in the blood sample obtained, fetal aneuploidy or maternal drug exposure to low-molecular weight heparins amongst other reasons.

Is Cell-free DNA Testing the Right Test for Me?

While some women are at a higher risk based on their age or personal or family history, every pregnancy has a risk of being affected with a chromosome abnormality. Hence, noninvasive prenatal testing is available to all women who are pregnant.

Deciding whether to pursue this test is a very personal decision. A lot of factors go into making this decision which are unique to each patient. Some patients might use the information to eventually make a decision about continuing the pregnancy and some others might pursue this testing just to get more information and be prepared for what is to come. There are also other testing options available during a pregnancy that test for the same conditions as NIPS – kindly speak with your provider or a genetic counselor to understand your options are and what tests are best suited based for you.

Genetic Counseling & Noninvasive Prenatal Testing

Multiple cell free DNA screening tests are available in the market today, and noninvasive prenatal testing is easier than ever. Each lab that offers this test, markets it under a unique name. Different cell-free DNA tests might screen for different conditions and even use different technologies for this testing. It is hence highly recommended that individuals undergoing this testing also pursue genetic counseling to understand both the benefits and the limitations of this test.

AT-GC’s team of highly trained and board-certified genetic counselors are always available to meet with you virtually to answer any related questions and help you make the decisions that are best for you.

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