Non-invasive prenatal testing (NIPT) screens for certain chromosomal anomalies in a fetus using a blood sample from the pregnant individual. MaterniT21 is a specific brand of NIPT, developed to identify potential genetic conditions early in pregnancy. It provides expectant parents with information about the likelihood of specific chromosomal abnormalities.
Chromosomal Conditions Screened
The MaterniT21 test primarily screens for common fetal aneuploidies, conditions caused by an atypical number of chromosomes. These include Trisomy 21, Trisomy 18, and Trisomy 13. It also screens for sex chromosome aneuploidies.
Trisomy 21, also known as Down syndrome, occurs when there is an extra copy of chromosome 21. Individuals with Down syndrome often experience developmental delays, mild to moderate intellectual disability, and distinct physical features. These can include a flattened face, upward-slanting almond-shaped eyes, and poor muscle tone.
Trisomy 18, or Edwards syndrome, results from an extra copy of chromosome 18. This condition is associated with severe intellectual disability and various physical abnormalities affecting organs like the heart, lungs, and kidneys. Many babies with Edwards syndrome have low birth weight and may have a small, abnormally shaped head or clenched fists with overlapping fingers.
Trisomy 13, known as Patau syndrome, is caused by an extra copy of chromosome 13. This rare condition leads to severe intellectual disability and significant physical abnormalities, often affecting the brain, heart, and face. Infants with Patau syndrome may have a cleft lip or palate, extra fingers or toes, and poorly developed eyes.
The test also screens for sex chromosome aneuploidies. These conditions include:
- Turner syndrome (45,X): Affects females, characterized by a missing or partially missing X chromosome, leading to short stature and ovarian dysfunction.
- Klinefelter syndrome (47,XXY): Affects males with an extra X chromosome, often resulting in reduced testosterone, infertility, and learning difficulties.
- Triple X syndrome (47,XXX): Affects females with an extra X chromosome, which may cause taller stature and an increased risk of learning disabilities.
- XYY syndrome (47,XYY): Affects males with an extra Y chromosome, sometimes associated with taller stature and learning or behavioral challenges.
How the Test Works
The MaterniT21 test analyzes cell-free DNA (cfDNA) found in the pregnant individual’s blood sample. During pregnancy, fragments of DNA from both the mother and the placenta circulate in the maternal bloodstream. These placental DNA fragments are typically identical to fetal DNA.
The laboratory isolates and analyzes these cfDNA fragments to detect specific chromosomal imbalances. It looks for an altered proportion of DNA from particular chromosomes, which can indicate an extra or missing chromosome in the fetus. For instance, an increased amount of DNA fragments from chromosome 21 suggests a higher likelihood of Trisomy 21.
A factor in this analysis is the “fetal fraction,” which refers to the percentage of cfDNA in the maternal blood that originates from the placenta. A sufficient fetal fraction, typically above 4%, is necessary for accurate test results. If the fetal fraction is too low, the test may not yield a result or could lead to an inaccurate outcome.
Who Should Consider the Test
MaterniT21 can be considered by any pregnant individual seeking information about their baby’s genetic health. It is particularly relevant for those with an increased likelihood of fetal chromosomal abnormalities. This includes individuals of advanced maternal age, typically defined as 35 years or older at the time of delivery. The likelihood of certain aneuploidies, such as Down syndrome, increases with maternal age.
Individuals with a personal or family history of chromosomal aneuploidies may consider this test. Other reasons include increased risk indicated by previous screening tests (like first-trimester or maternal serum screening) or abnormal ultrasound findings suggestive of aneuploidy. The test can be performed as early as 10 weeks of gestation, providing information earlier in pregnancy.
Interpreting Test Results
Understanding MaterniT21 results involves recognizing it is a screening test, not a diagnostic one. This means it estimates the likelihood of a condition rather than providing a definite diagnosis. Results are typically reported as “low risk” (negative), “high risk” (positive), or “no result” or “inconclusive.”
A “low risk” result suggests a decreased likelihood of the screened conditions, but it does not completely rule out an abnormality. A “high risk” result indicates an increased probability that the fetus has one of the screened chromosomal conditions. However, a high-risk result does not confirm a diagnosis; further diagnostic testing is recommended for confirmation.
Diagnostic tests, such as amniocentesis or chorionic villus sampling (CVS), analyze fetal cells directly and provide a definitive answer. While NIPTs like MaterniT21 have high accuracy, they are not 100% precise. False positives (a high-risk result when the fetus is unaffected) and false negatives (a low-risk result when the fetus is affected) can occur in rare instances.
In cases of an inconclusive or no result, which can happen due to a low fetal fraction or other technical reasons, a repeat blood draw may be suggested. Regardless of the outcome, genetic counseling is important to discuss the implications of the results, understand options for further testing, and make informed decisions about pregnancy care.