Natera’s Panorama prenatal screening test is highly accurate for the most common chromosomal conditions, detecting over 99% of Down syndrome cases with a false positive rate below 0.1%. But “highly accurate” doesn’t mean diagnostic, and the distinction matters. Several biological factors can shift those numbers for individual pregnancies, making some results more reliable than others.
Detection Rates for Common Trisomies
Panorama screens for three major chromosomal conditions: trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Across large clinical studies, cell-free DNA tests like Panorama consistently detect trisomy 21 with a pooled sensitivity of 99.3% and a false positive rate as low as 0.06%. For trisomy 18, sensitivity runs around 97.4%, and trisomy 13 falls in a similar range, though with slightly wider confidence intervals because fewer pregnancies are affected.
Specificity for all three trisomies is approximately 99.9%, meaning that when the test says your pregnancy is low-risk, it’s almost certainly correct. These numbers make cell-free DNA screening significantly more accurate than older approaches using blood markers and ultrasound measurements, which is why the American College of Obstetricians and Gynecologists now recommends it as the most sensitive and specific screening option for these three conditions in any patient population.
Screening vs. Diagnostic Testing
Even with 99%+ detection rates, Panorama remains a screening test rather than a diagnostic one. The practical difference: a high-risk result does not confirm your baby has a chromosomal condition. It means the probability is elevated enough to warrant follow-up with amniocentesis or chorionic villus sampling, which analyze actual fetal cells and provide a definitive answer.
The reason screening can’t be diagnostic comes down to biology. Cell-free DNA tests analyze tiny fragments of placental DNA circulating in your blood. The placenta and the fetus usually share the same genetic makeup, but not always. A phenomenon called confined placental mosaicism, where the placenta carries a chromosomal abnormality that the fetus doesn’t, is one of the most common reasons for false positive results. Maternal factors, including copy number variants in the pregnant person’s own DNA, can also trigger a misleading result.
The positive predictive value (the chance a high-risk result is truly positive) varies based on how common the condition is in your age group. For a 35-year-old receiving a high-risk result for Down syndrome, the chance the result is a true positive is much higher than for a 25-year-old, simply because the baseline prevalence is higher. Your provider can help you understand what a high-risk result means for your specific situation.
How Body Weight Affects Results
Maternal weight is one of the biggest factors influencing whether Panorama can return a result at all. The test requires a minimum concentration of placental DNA in your blood, known as fetal fraction. Below roughly 4% to 6%, the test can’t reliably distinguish fetal DNA from maternal DNA, and the lab will report a “no call” instead of a result.
Fetal fraction drops as maternal weight increases. In one large study, women under 150 pounds had a no-call rate of just 0.14% when tested between 9 and 12 weeks. Women over 250 pounds saw failure rates exceeding 10%, and for those over 350 pounds, more than half of initial draws failed to produce a result. The biological explanation: higher body weight increases the total volume of blood and the amount of maternal DNA shed from fat tissue, both of which dilute the placental signal.
Waiting a few extra weeks can help. Fetal fraction rises as pregnancy progresses, so drawing blood at 13 to 18 weeks instead of 9 to 12 weeks reduces no-call rates. Women over 400 pounds, for instance, saw their no-call rate drop from 17.4% to 6.5% by waiting until after 13 weeks. If you receive a no-call result, a redraw at a later gestational age is typically the first step.
Accuracy in Twin Pregnancies
Testing twins adds complexity because there may be two genetically distinct placentas contributing DNA to the maternal bloodstream. Most cell-free DNA platforms struggle with this, but Panorama uses a technology called SNP-based analysis that can distinguish between identical and fraternal twins. A prospective validation study published in the Journal of Clinical Medicine reported 100% accuracy for determining zygosity (whether twins are identical or fraternal), fetal sex, and chromosomal abnormalities as early as 9 weeks.
ACOG recommends cell-free DNA as a first-line screening option for trisomy 21 in twin pregnancies, and notes that detection rates for trisomies 18 and 13 also appear consistently high in twins. However, screening for sex chromosome abnormalities in twin pregnancies is not recommended due to limited data.
Where Accuracy Drops: Microdeletions and Rare Findings
Beyond the three common trisomies, Panorama offers optional screening for microdeletion syndromes, including 22q11.2 deletion (DiGeorge syndrome), and sex chromosome abnormalities like Turner syndrome or Klinefelter syndrome. The accuracy for these conditions is notably lower than for trisomies 21, 18, and 13.
ACOG does not recommend routine screening for microdeletion conditions in the general population. Their guidance states that patients interested in information about fetal copy number variants should be offered diagnostic testing (amniocentesis or CVS) rather than cell-free DNA screening. If you do opt into 22q11.2 screening, ACOG recommends doing so only after thorough pretest counseling, because the lower prevalence of these conditions means positive predictive values are much lower. A high-risk result for a microdeletion is more likely to be a false alarm than a high-risk result for Down syndrome.
Sex chromosome screening is offered as an opt-in with appropriate counseling. The detection rates are generally good, but false positives are more common than with autosomal trisomies, and the clinical significance of some sex chromosome findings (like an extra X or Y chromosome) can be mild or variable, making interpretation more nuanced.
Natera’s Cancer Testing: Signatera
Natera also offers Signatera, a blood test designed to detect residual cancer DNA after treatment. This test works differently from Panorama. It creates a personalized genetic profile from a patient’s tumor, then searches for those specific DNA fragments in blood draws over time. In analytical validation using healthy subjects, Signatera achieved 99.8% specificity, meaning it rarely flags cancer when none is present. Clinical performance data across breast cancer, lung cancer, melanoma, and kidney cancer are being evaluated in real-world cohorts of over 300 patients, though detailed sensitivity numbers by cancer type are still emerging.
What Affects Your Individual Accuracy
The headline accuracy numbers from clinical studies represent averages across thousands of pregnancies. Your personal accuracy depends on several factors working together: gestational age at the time of the blood draw, your body weight, whether you’re carrying one baby or multiples, which conditions you’re screening for, and your age-related baseline risk. A singleton pregnancy in a person of average weight, drawn after 10 weeks and screened only for the three common trisomies, will get the most reliable result the test can offer.
The further you move from that scenario, the more important it becomes to understand the test’s limitations. A no-call result is not a negative result. A high-risk result is not a diagnosis. And a low-risk result, while very reassuring, does not guarantee a chromosomally typical pregnancy. Panorama is the most accurate prenatal screening tool currently available, but the word “screening” still carries real meaning.