NIPT Aneuploidy Screen (Cell-Free DNA)

A prenatal blood test that estimates the chance that a baby has an extra copy of chromosome 21, 18 or 13. It is a screening test, not a diagnosis.

AI-verified against cited sources. Awaiting expert reviewAlso called NIPT, NIPS, cfDNALOINC 73967-2

What it is

Cell-free DNA screening, also called NIPT or NIPS, looks at tiny fragments of DNA from the placenta that float in a pregnant person's blood. The lab uses them to estimate the chance that the baby has an extra copy of chromosome 21, 18 or 13, which cause Down, Edwards and Patau syndromes. Some labs also report sex chromosome results. It can be done from about 9 or 10 weeks of pregnancy. It is a screening test, so it estimates chance and does not give a final yes or no.

Why it matters

Most results come back low risk. A low-risk result makes these conditions unlikely, but it does not rule them out or check for every health problem. A high-risk result is not a diagnosis, because placental DNA is sometimes different from the baby's own, so false alarms happen. Only a diagnostic test, CVS or amniocentesis, can say for sure. Professional groups such as ACMG and SMFM support offering this test to everyone who is pregnant, and every patient can choose to have it or not.

If it’s high

A high-risk (positive) result means the screen found a pattern that goes with an extra or missing chromosome. It does not mean the baby has the condition. How likely a high-risk result is to be correct depends on the condition and on age. It is lower in younger people, and lower for trisomy 18 and trisomy 13 than for trisomy 21. The usual next steps are genetic counseling, a detailed ultrasound, and an offer of diagnostic testing with CVS or amniocentesis, which look at the baby's cells directly. Diagnostic testing is how to know for sure before making big decisions.

Common causes

The baby truly has the extra or missing chromosome, which becomes more likely with older age in pregnancy
A change in the placenta's chromosomes that is not in the baby (confined placental mosaicism)
A twin that did not continue (a vanishing twin)
A chromosome change in the pregnant person's own cells that has no health effect
Less often, a past transplant, a recent blood transfusion, fibroids, a maternal health condition, statistical chance or a technical error

What can help

Ask for genetic counseling, which is usually offered after a high-risk result
Ask about a detailed ultrasound and about diagnostic testing (CVS or amniocentesis) to confirm the result
Ask how likely the result is to be correct for your age and for the condition named on your report

What can affect your result

How far along the pregnancy is: results can be reported from about 9 to 10 weeks, and the share of baby DNA in your blood grows as pregnancy goes on
Body weight: a higher weight can lower the share of baby DNA and make a 'not reportable' result more likely
Twins and other multiples: results are read differently, and a vanishing twin can cause a false positive
Your own health and history: a past transplant, recent blood transfusion, lupus, cancer, low-molecular-weight heparin, assisted reproduction or a donor egg
Which lab you use: the wording differs ('positive', 'high risk', 'aneuploidy detected', 'aneuploidy suspected') and so do the conditions included
A higher body weight, a very early draw (before about 9 or 10 weeks) and other causes of a low share of baby DNA in your blood can lead to a 'not reportable' result.
A twin pregnancy, including a twin that did not continue (a 'vanishing twin'), can change how results are read and can cause a false-positive result.
Chromosome changes in the pregnant person's own cells, a past organ or stem cell transplant, a recent blood transfusion, fibroids, or rarely a cancer can cause an unexpected or false-positive result.
Low-molecular-weight heparin and conditions such as lupus are linked with 'not reportable' results. Do not stop any medicine on your own.
Assisted reproduction (such as IVF), donor eggs, and changes in the placenta that are not in the baby (confined placental mosaicism) can also affect the result.
Lab handling: for MaterniT21 PLUS the draw must be at 9 weeks or later into a special 10 mL preservative (Streck) tube that reaches the lab within 72 hours, and the lab needs your height, weight, number of babies and weeks of pregnancy.

The result reflects the current pregnancy. The test can be done from about 9 to 10 weeks.

When to talk to a clinician

A high-risk or 'not reportable' result is not an emergency, but follow-up is time sensitive. Contact your prenatal clinician promptly to talk about confirming the result, because diagnostic tests are done within certain weeks of pregnancy (CVS between weeks 10 and 13, amniocentesis usually between weeks 15 and 20).

Questions you could ask

Which conditions did this screen include, and which does it not cover?
Could twins, my weight or a health condition I have affect my result?
How likely is this high-risk result to be correct for my age and for this condition?
Should we talk with a genetic counselor and consider a diagnostic test?
What would a detailed ultrasound add?

Questions people ask

My result says 'low risk.' Does that mean my baby is fine?

A low-risk result makes Down, Edwards and Patau syndromes unlikely, but no screening test is perfect, and it does not look for every health condition. Your prenatal care, including ultrasounds, continues as planned.

My result says 'high risk' or 'positive.' Is the diagnosis certain?

No. This is a screening test. How likely a positive result is to be correct depends on the condition and on age. SMFM's estimates for trisomy 21 run from about 48 in 100 at age 20 to about 93 in 100 at age 40, and are lower for trisomy 18 and trisomy 13. Genetic counseling and a diagnostic test (CVS or amniocentesis) can confirm or rule out the result.

What does 'no result' or 'not reportable' mean?

The lab could not get a reliable answer, most often because the share of baby DNA in the blood was too low. This is not a result in either direction. It can happen with an early draw or a higher body weight, among other reasons, and in rare cases it points to something else going on, so your clinician will talk through options.

Show the science and sources

For clinicians and researchers

Cell-free DNA (cfDNA) screening analyzes short placental-derived fragments (about 142 base pairs) in maternal plasma. The fetal fraction is generally 10% to 20% of total cfDNA at its peak between 10 and 21 weeks, and most labs need at least 2% to 4%. Reported performance (SMFM Consult Series #74, Table 2): trisomy 21 sensitivity 99.2% and specificity 99.91%; trisomy 18, 96.3% and 99.87%; trisomy 13, 91% and 99.87%; 45,X, 90.3% and 99.77%. The positive predictive value depends on prevalence, so on maternal age: for trisomy 21 it ranges from 48% at age 20 to 93% at age 40, for trisomy 18 from 14% to 69%, for trisomy 13 from 6% to 50%, and for 45,X it stays near 32% at every age. Reporting language varies by lab (positive, high risk, aneuploidy detected, aneuploidy suspected) and can wrongly imply that the test is diagnostic. Causes of false-positive results include mosaicism in the fetus, placenta or patient, maternal copy number variants, a demised twin, maternal malignancy, previous transplant, fibroids, recent blood transfusion, statistical chance and technical error. Nonreportable results (also called no call, no result, low fetal fraction or test failure) occurred in 0.03% to 11.1% of tests across studies and about 0.85% in the ACMG evidence review, and are linked with obesity, early gestation, aneuploidy, low-molecular-weight heparin use, lupus, antiphospholipid syndrome, malignancy, assisted reproduction, donor egg, confined placental mosaicism and twin gestation. Offering fetal diagnostic testing is the first step for any abnormal or inconclusive result. The ACMG 2023 guideline strongly recommends NIPS over traditional screening methods for all pregnant patients with singleton and twin gestations for trisomies 21, 18 and 13. SMFM (2025) recommends that cfDNA screening for these trisomies be routinely available to all obstetric patients, that sex chromosome aneuploidy screening be offered as an opt-in choice, and that routine screening for microdeletions not be done. ACOG Practice Bulletin 226 (2020) reviews the screening options. The US FDA issued a public warning on 19 April 2022 about the risk of false-positive results and inappropriate interpretation (as described by SMFM). Fetal sex and fetal fraction are reported by some labs but are separate markers here.

LOINC 73967-2 (primary), 92901-8, 77014-9, 77015-6, 79211-9. Specimen: plasma.

Sources

Society for Maternal-Fetal Medicine Consult Series #74: Cell-free DNA screening for aneuploidies: Updated guidance, Pregnancy (Wiley), for the Society for Maternal-Fetal Medicine (2025)
Noninvasive prenatal screening (NIPS) for fetal chromosome abnormalities in a general-risk population: An evidence-based clinical guideline of the American College of Medical Genetics and Genomics (ACMG), Genetics in Medicine (2023)
Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin Summary, Number 226, Obstetrics & Gynecology (2020)
MaterniT21 Plus (test FMT21, Sequenom Center for Molecular Medicine), Mayo Clinic Laboratories Extended Catalog
Prenatal Cell-Free DNA Screening, MedlinePlus Medical Tests, National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.