Noninvasive prenatal testing (NIPT) analyzes circulating cell-free DNA extracted from a maternal blood sample. It is used to screen for Down syndrome (trisomy 21), Edwards syndrome (Trisomy 18), Patau syndrome (trisomy 13), XY anomalies, selected microdeletions (DiGeorge, 1p36 deletion, Smith-Magenis, Wolf-Hirschhorn), and fetal gender by analyzing the baby's DNA in the mother’s blood.
The VERACITY Core test is a noninvasive prenatal test (NIPT) that detects fetal autosomal aneuploidies and can determine the fetus's gender. It can be carried out from the 10th week of pregnancy.
The VERACITY Core checks for autosomal aneuploidies:
- Down syndrome (Trisomy 21)
- Edwards syndrome (Trisomy 18)
- Patau syndrome (Trisomy 13)
The gender of the fetus may be determined as an option.
More Information
Noninvasive prenatal testing (NIPT) is a method of determining the risk that the fetus will be born with specific genetic abnormalities. This testing analyzes small DNA fragments circulating in a pregnant woman’s blood. Unlike most DNA found inside a cell’s nucleus, these fragments are free-floating and not within cells, called cell-free DNA (cfDNA). These tiny fragments usually contain fewer than 200 DNA base pairs and arise when cells die off and get broken down, and their contents, including DNA, are released into the bloodstream.
During pregnancy, the mother’s bloodstream contains a mix of cfDNA from her cells and cells from the placenta. The placenta is tissue in the uterus that links the fetus and the mother’s blood supply. Placental cells are shed into the mother’s bloodstream throughout pregnancy. The DNA in placental cells is usually identical to the DNA of the fetus. Analyzing cfDNA from the placenta allows early detection of specific genetic abnormalities without harming the fetus.
Noninvasive prenatal testing (NIPT) is most often used to look for chromosomal disorders caused by the presence of an extra or missing copy (aneuploidy) of a chromosome. NIPT primarily looks for Down syndrome (trisomy 21, caused by an extra chromosome 21), trisomy 18 (caused by an extra chromosome 18), trisomy 13 (caused by an extra chromosome 13), and extra or missing copies of the X chromosome and Y chromosome (the sex chromosomes). The accuracy of the test varies by disorder.
NIPT may include screening for additional chromosomal disorders caused by missing (deleted) or copied (duplicated) chromosome sections. NIPT is beginning to be used to test for genetic disorders caused by changes (variants) in single genes.
NIPT is considered noninvasive because it requires drawing blood only from the pregnant woman and does not pose any risk to the fetus.
NIPT is a screening test, meaning it will not give a definitive answer about whether or not a fetus has a genetic condition. The test can only estimate whether the risk of having certain conditions is increased or decreased. In some cases, NIPT results indicate an increased risk for a genetic abnormality when the fetus is unaffected (false positive), or the results indicate a decreased risk for a genetic abnormality when the fetus is affected (false negative). Because NIPT analyzes both fetal and maternal cfDNA, the test may detect a genetic condition in the mother.
Enough fetal cfDNA must be in the mother’s bloodstream to identify fetal chromosome abnormalities. The proportion of cfDNA in maternal blood from the placenta is the fetal fraction. Generally, the fetal fraction must be above 4 percent, typically around the tenth week of pregnancy. Low fetal fractions can lead to an inability to perform the test or a false negative result. Reasons for low fetal fractions include testing too early in the pregnancy, sampling errors, maternal obesity, and fetal abnormality.
There are multiple NIPT methods to analyze fetal cfDNA. The most common method to determine chromosomal aneuploidy is to count all cfDNA fragments (fetal and maternal). If the percentage of cfDNA fragments from each chromosome is as expected, then the fetus has a decreased risk of having a chromosomal condition (negative test result). If the percentage of cfDNA fragments from a particular chromosome is more than expected, the fetus is more likely to have a trisomy condition (positive test result). A positive screening result indicates that further testing should be performed to confirm the result.
Cautions
- VERACITY is available for singleton and twin pregnancies, including in-vitro fertilization (IVF) pregnancies, with a gestation of at least 10 weeks.
- Twin pregnancies in which the loss of one fetus occurred (vanished twin) are eligible for testing after the 10th week of gestation and four weeks after the vanishing event. Information about the number of fetuses and IVF status is mandatory and affects testing.
- Twin and vanishing twin pregnancies are not eligible for X and Y aneuploidy detection.
- Patients with confirmed malignancy or a history of malignancy and patients with bone marrow or organ transplants are not eligible for the test.
- In cases of insufficient fetal DNA in the maternal blood (low fetal fraction), blood sampling may be performed later during the pregnancy, and the test may be repeated (recommended at least three weeks after the initial blood sample).
- The VERACITY non-invasive prenatal test is not intended or validated for detecting mosaicism, triploidy, partial trisomy, or translocations.
- A positive result for twin pregnancies indicates a high risk of at least one affected fetus. In twin pregnancies, detection of Y chromosomal DNA indicates the presence of at least one Y chromosome.
- Although this test is highly accurate, false positive and false negative results are still possible. This can have technical and/or biological causes (e.g., confined placental mosaicism (CPM) or other types of mosaicism, maternal constitutional or somatic chromosomal abnormalities, residual cfDNA from a vanished twin, or other rare molecular events).
- The test will not identify all deletions associated with each microdeletion syndrome. This test has been validated for deletions mapped over the whole length of the typical genomic deletion area and may be unable to detect minor and cryptic deletions.
- The VERACITY test is not diagnostic; it is a screening test, and results should be considered in the context of other clinical criteria.
- The referring physician is responsible for counseling before and after the test, including advice regarding the need for additional prenatal invasive genetic testing.
- It is recommended that a positive result is confirmed by amniocentesis.
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