MaterniT21 PLUS results are reported as either “no aneuploidy detected” (negative) or “aneuploidy detected” (positive) for each condition the test screens. You won’t see a percentage risk score or a probability chart. The report uses straightforward language designed to give you a clear answer for each chromosome evaluated, though understanding what those answers actually mean, and what they don’t mean, takes a bit more context.
What the Report Screens For
The core panel evaluates the three most common trisomies: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Each one gets its own line on the report with a separate result.
Beyond those three, the test also evaluates sex chromosome conditions in singleton pregnancies. These include Turner syndrome (45,X), Klinefelter syndrome (47,XXY), Triple X syndrome (47,XXX), and XYY syndrome. Sex chromosome findings are handled differently from the core trisomies. They are only reported when an abnormality is detected. If everything looks typical, you simply won’t see a separate callout for them.
The enhanced sequencing panel screens for several rare microdeletions and additional trisomies. These include 22q (DiGeorge syndrome), 5p (Cri-du-chat syndrome), 1p36 deletion syndrome, 15q (which covers both Prader-Willi and Angelman syndromes), 11q (Jacobsen syndrome), 8q (Langer-Giedion syndrome), 4p (Wolf-Hirschhorn syndrome), trisomy 16, and trisomy 22. Like the sex chromosome results, microdeletion findings typically appear on the report only when something abnormal is flagged.
How Negative Results Are Reported
A negative result for the core trisomies will read something like “no aneuploidy detected” next to each chromosome number. This means the amount of DNA from that chromosome in your blood sample fell within the expected range. It does not guarantee the baby is unaffected, but the test is highly accurate for these conditions. In validation studies, sensitivity for trisomy 21 was 100%, with a false positive rate of just 0.1%.
For sex chromosomes, a negative result often isn’t stated explicitly. Instead, you’ll see a line about Y chromosome detection. If the report says “No Y chromosomal material detected,” that is consistent with a female fetus. If Y material is detected, the fetus is likely male. The absence of any additional sex chromosome finding means no aneuploidy was identified in that area.
How Positive Results Are Reported
A positive result will state that aneuploidy was detected for a specific chromosome. If the enhanced panel flags something, it appears under a section labeled “Additional Finding.” The report names the condition directly, so you’ll see references to a specific trisomy or microdeletion rather than a vague risk category.
Positive results on this test are not a diagnosis. MaterniT21 is a screening test, which means it identifies pregnancies at higher risk. For trisomy 21, the positive predictive value is about 97.9%, meaning roughly 98 out of 100 people who get a positive result for Down syndrome truly have an affected pregnancy. That also means about 2 out of 100 positive results are false alarms.
The accuracy varies by condition. In validation data, there were no false positives for trisomies 18 or 13, giving those results a positive predictive value of 100% in that study. However, there were a small number of false negatives: three missed cases of trisomy 18 and two missed cases of trisomy 13. The rarer microdeletion results generally have lower positive predictive values than the core trisomies, which means a positive flag for something like 22q or 1p36 has a higher chance of being a false positive compared to a trisomy 21 result.
What a “No Call” Result Means
Sometimes the lab cannot produce a result at all. This is called a “no call” or “no result” and it means the test was uninterpretable. Common reasons include not enough fetal DNA in the blood sample (which can happen if the blood was drawn too early or if your body mass index is higher) or technical issues during sequencing.
A no-call result is not the same as a negative. The American College of Obstetricians and Gynecologists notes that test failure is associated with an increased risk of aneuploidy. If you receive a no-call result, your provider will typically discuss whether to redraw your blood for a second attempt or move directly to diagnostic testing.
Fetal Sex on the Report
The report includes a line for Y chromosome detection, which effectively tells you the fetal sex. “Y chromosomal material detected” points to a male fetus, while “No Y chromosomal material detected” points to a female fetus. This is one of the most straightforward parts of the report and is generally very reliable, since it’s based on the presence or absence of Y chromosome DNA in your bloodstream.
In twin pregnancies, the sex result can be less clear-cut. If Y material is detected, at least one fetus is male, but the test cannot determine which twin carries it or whether both do.
What Happens After a Positive Result
Any positive screening result should be confirmed with a diagnostic test before making decisions about the pregnancy. The two options are chorionic villus sampling (CVS), which can be performed between about 10 and 13 weeks, and amniocentesis, typically done after 15 weeks. Both involve collecting a small sample of fetal cells and analyzing the actual chromosomes, giving you a definitive yes or no.
ACOG recommends that anyone with a positive result receive genetic counseling along with a comprehensive ultrasound evaluation. A genetic counselor can walk you through what the specific condition means, how reliable the screening result is for that particular finding, and what your options are going forward. Many hospitals and maternal-fetal medicine offices have genetic counselors on staff, and your OB can refer you if the office doesn’t.
If your result is positive for one of the rarer microdeletions, genetic counseling becomes especially important. Because these conditions are less common in the general population, even a highly specific test produces more false positives for rare conditions than for common ones. A counselor can help you understand what the actual probability is for your specific result before you decide on next steps.
Factors That Can Affect Accuracy
MaterniT21 analyzes fragments of DNA circulating in your blood. Most of the fetal DNA in your bloodstream actually comes from the placenta, not directly from the baby. In rare cases, the placenta and the baby have different genetic makeups, a situation called confined placental mosaicism. This can cause a false positive (the placenta has the trisomy but the baby doesn’t) or, less commonly, a false negative.
Twin pregnancies and pregnancies where one twin stopped developing early (sometimes called a vanishing twin) can also skew results. The DNA from the nonviable twin may still circulate in your blood and interfere with the analysis. ACOG specifically flags this scenario as carrying a significant risk of inaccurate results, and diagnostic testing is recommended.
Maternal conditions can occasionally affect results too. Certain chromosomal changes in the mother’s own cells, including some that are harmless, can produce unexpected findings on the report. This is another reason a positive result calls for confirmation rather than immediate conclusions.