MaterniT21 is a prenatal blood test that screens for Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), sex chromosome conditions, and select microdeletion syndromes. It works by analyzing fragments of your baby’s DNA that circulate naturally in your bloodstream during pregnancy. The test can be done as early as 9 weeks of gestation, and results typically come back within 5 to 7 days.
The Three Main Trisomies
The core purpose of MaterniT21 is screening for the three most common chromosomal trisomies, conditions where a baby has three copies of a chromosome instead of the usual two.
Trisomy 21 (Down syndrome) is the most common chromosomal condition in live births and the primary target of the test. In clinical validation studies involving nearly 1,700 samples, MaterniT21 correctly identified 210 out of 212 Down syndrome cases, for a sensitivity of 99.1% and a specificity of 99.9%. That means it catches almost every true case while producing very few false alarms.
Trisomy 18 (Edwards syndrome) causes severe developmental problems, and most affected pregnancies do not survive to term. The test’s detection rate for trisomy 18 is even higher: in a study of nearly 2,000 samples, it identified all 59 confirmed cases, with sensitivity above 99.9% and specificity of 99.6%.
Trisomy 13 (Patau syndrome) is the rarest of the three and also carries a very poor prognosis. Detection is slightly less precise here. The same study found the test caught 11 of 12 cases, a sensitivity of 91.7% with specificity of 99.7%. That’s still far more accurate than older screening methods like the first-trimester combined screen, but it means roughly 1 in 12 trisomy 13 cases could be missed.
Sex Chromosome Conditions
Beyond the three main trisomies, MaterniT21 also screens for conditions involving the X and Y chromosomes. These include Turner syndrome (where a girl has only one X chromosome instead of two), Klinefelter syndrome (where a boy has an extra X chromosome), Triple X syndrome, and XYY syndrome. Sex chromosome conditions are generally less severe than trisomies 13 or 18, and many people with them live full, healthy lives with minimal or no symptoms. Still, early awareness can help with planning for developmental support if needed.
Because the test reads sex chromosomes, it also reveals fetal sex. Your provider will typically ask whether you want that information included in your results.
Microdeletion Syndromes
The expanded MaterniT21 PLUS panel can also screen for microdeletions, which are tiny missing segments of a chromosome. The most well-known is 22q11.2 deletion syndrome (also called DiGeorge syndrome), which can cause heart defects, immune problems, and learning difficulties. Other microdeletions on the panel include those associated with Cri-du-chat syndrome, Prader-Willi syndrome, and Angelman syndrome.
It’s worth knowing that microdeletion screening is less accurate than trisomy screening. These conditions are rarer, and the smaller the chromosomal change, the harder it is to detect from fragments of DNA in your blood. A positive result for a microdeletion carries a higher chance of being a false positive compared to a trisomy result, so confirmatory testing through amniocentesis or chorionic villus sampling (CVS) is especially important before making any decisions.
How the Test Works
Starting early in pregnancy, small fragments of DNA from the placenta shed into your bloodstream. These fragments, called cell-free fetal DNA, mix with your own cell-free DNA. MaterniT21 uses a technology called massively parallel sequencing to count millions of these DNA fragments and determine whether there are more copies from any particular chromosome than expected. If the count from chromosome 21 is slightly elevated, for example, it suggests the baby may have Down syndrome.
For the test to produce a reliable result, enough of the DNA in your blood sample needs to come from the pregnancy rather than from you. This proportion, called the fetal fraction, typically needs to be between 2% and 4% depending on the specific method used. Most pregnant people reach that threshold by 9 to 10 weeks, which is why the test can be offered so early. In some cases, factors like higher body weight can lower the fetal fraction, and the lab may need to request a repeat blood draw a week or two later.
What the Results Mean
MaterniT21 is a screening test, not a diagnostic test. That distinction matters. A “positive” or “high-risk” result means there’s an increased probability your baby has the condition, not a certainty. Similarly, a “negative” or “low-risk” result makes the condition very unlikely but doesn’t guarantee the baby is unaffected.
For trisomies 21 and 18, the false-positive rate is extremely low (under 1%), so a positive result carries significant weight. But even with those numbers, whether a positive result truly reflects an affected pregnancy depends on your age and background risk. For a 25-year-old with a positive trisomy 21 result, the chance it’s a true positive is lower than for a 40-year-old with the same result, simply because Down syndrome is less common in younger pregnancies.
If your screening comes back positive for any condition, your provider will offer diagnostic testing. Amniocentesis (typically done around 15 to 20 weeks) or CVS (done around 10 to 13 weeks) can confirm or rule out the finding by directly analyzing the baby’s chromosomes. These procedures carry a small risk of miscarriage, roughly 1 in 300 to 1 in 500, which is why screening tests like MaterniT21 exist as a first step to help you decide whether invasive testing is warranted.
Timing and Logistics
The test requires a standard blood draw from your arm. It can be ordered as early as 9 weeks of pregnancy and performed at any point after that. Results typically arrive 5 to 7 days after the lab receives your sample. Your provider’s office will usually call you with the results or make them available through an online patient portal.
Insurance coverage varies. Many plans cover the test for pregnancies considered higher risk due to maternal age (35 or older), abnormal ultrasound findings, or a previous pregnancy affected by a chromosomal condition. Some insurers now cover it for all pregnancies regardless of risk factors, but out-of-pocket costs can range from under $100 to several hundred dollars depending on your plan. Labcorp, which manufactures MaterniT21, offers financial assistance programs for patients who qualify.