Yes, several prenatal tests can detect Down syndrome, and they fall into two categories: screening tests that estimate your risk, and diagnostic tests that give a definitive answer. Screening is available as early as 10 weeks into pregnancy. Diagnostic testing can confirm or rule out Down syndrome with near-complete certainty but involves a needle procedure. Current guidelines from major medical organizations recommend that all pregnant people be offered the option to screen for Down syndrome regardless of age or risk factors.
Screening Tests vs. Diagnostic Tests
The distinction matters because the two types of tests answer different questions. A screening test tells you whether your pregnancy has a higher or lower chance of Down syndrome. It cannot tell you for sure. A diagnostic test analyzes actual chromosomes from the pregnancy and can confirm whether an extra copy of chromosome 21 is present.
Screening tests carry no physical risk to the pregnancy. They use blood draws and ultrasound. Diagnostic tests require collecting a small sample of placental tissue or amniotic fluid with a needle, which carries a small risk of pregnancy loss. Most people start with screening and only move to diagnostic testing if the results come back high-risk or if they want a definitive answer from the start.
Cell-Free DNA Screening (NIPT)
The most accurate screening option is cell-free DNA testing, commonly called NIPT (noninvasive prenatal testing). It works by analyzing tiny fragments of DNA from the placenta that circulate in your blood. A simple blood draw is all that’s needed, and it can be done starting around 10 weeks of pregnancy.
For Down syndrome specifically, NIPT has a pooled sensitivity of 99.3% and a specificity of 99.9%, based on a meta-analysis of 40 studies published in BMJ Open. That means it catches virtually all cases and very rarely flags a pregnancy that isn’t affected. Still, it is a screening test. A small number of results will be false positives, meaning the test says high-risk when the baby does not actually have Down syndrome.
False positives happen for real biological reasons. The most common is confined placental mosaicism, where the placenta has a chromosomal difference that the baby does not share. Other causes include a vanishing twin (a second embryo that stopped developing early but still releases DNA), certain uterine growths, or rarely, an undiagnosed maternal condition. Because of these possibilities, a high-risk NIPT result should always be followed up with a diagnostic test before making any decisions.
First Trimester Combined Screening
Available between weeks 11 and 13, this approach combines a blood test with a specialized ultrasound. The ultrasound measures the fluid-filled space at the back of the baby’s neck, called nuchal translucency. A larger-than-typical measurement can signal a higher chance of chromosomal conditions.
The blood test checks levels of three substances: a pregnancy hormone (hCG), a protein produced by the placenta (PAPP-A), and alpha-fetoprotein (AFP). Your provider combines these results with the ultrasound measurement and your age to calculate a risk estimate. This test is less accurate than NIPT but has been widely used for decades and is often offered alongside or as an alternative to cell-free DNA screening.
Second Trimester Quad Screen
If you missed first trimester screening or want additional information, a quad screen can be done between about 15 and 20 weeks. This blood test measures four substances: AFP, hCG, a form of estrogen called estriol, and a hormone called inhibin-A.
When Down syndrome is present, the pattern is distinctive: AFP and estriol tend to be lower than average, while hCG and inhibin-A tend to be higher. Your provider plugs these levels into a formula along with your age and gestational timing to generate a risk number. The quad screen is less sensitive than NIPT, so it catches fewer cases and produces more false positives, but it remains an option when earlier screening wasn’t done.
Diagnostic Testing: CVS
Chorionic villus sampling (CVS) is the earliest diagnostic option, typically performed between 10 and 12 weeks. A doctor uses either a thin catheter through the cervix or a needle through the abdomen to take a tiny sample of placental tissue. Because the placenta and baby develop from the same fertilized egg, the chromosomes in the sample reflect the baby’s genetic makeup.
The cells are then analyzed in a lab to count chromosomes and look for an extra copy of chromosome 21. This test is definitive. The main trade-off is a small risk of pregnancy loss. Recent cohort data puts the procedure-related loss rate below 0.5%, and a study in the Slovenian Journal of Public Health found a total loss rate of about 1% after CVS, which was actually slightly lower than the rate in a matched control group of women who did not have the procedure. The risk decreases when the procedure is done at 10 weeks or later by an experienced provider.
Diagnostic Testing: Amniocentesis
Amniocentesis can be performed from 15 weeks onward. A needle is guided by ultrasound through the abdomen to withdraw a small amount of amniotic fluid, which contains cells shed by the baby. Those cells are grown in a lab for up to 10 days, then examined under a microscope to check the number and appearance of every chromosome.
A rapid test can return results for Down syndrome in a day or two and is described as almost 100% accurate. The full chromosome analysis takes longer but provides a complete picture. The procedure-related risk of pregnancy loss is very low. In one large cohort study, the loss rate after amniocentesis was 0.8%, and when compared to matched controls, the procedure-attributable risk was estimated below 0.5%. In experienced hands, some centers report an attributable risk as low as 0.13%.
When Each Test Happens
The timeline of available tests follows the progression of pregnancy:
- Weeks 10 to 13: NIPT (cell-free DNA blood draw) and CVS (diagnostic) become available. First trimester combined screening with nuchal translucency ultrasound is offered between weeks 11 and 13.
- Weeks 15 to 20: Amniocentesis becomes available at 15 weeks. The quad screen blood test is typically drawn around 16 to 18 weeks.
- Weeks 18 to 22: A detailed anatomy ultrasound can identify physical markers sometimes associated with Down syndrome, though this is not a definitive test on its own.
You don’t need to have every test. The path depends on your preferences, your risk factors, and what your initial screening results show. Some people choose NIPT alone and only pursue amniocentesis or CVS if the result is high-risk. Others skip screening entirely and go straight to a diagnostic test for certainty. Your provider can help you decide which combination fits your situation.
What a Positive Screening Result Means
A high-risk screening result does not mean your baby has Down syndrome. It means the probability is elevated enough that diagnostic testing is recommended. Even with NIPT’s high accuracy, the chance that a positive result is a true positive depends heavily on your baseline risk. For a younger person with no other risk factors, the majority of positive NIPT results may still turn out to be false alarms after diagnostic confirmation.
This is why no irreversible decision should be based on screening alone. If you receive a high-risk result, the next step is CVS or amniocentesis to get a definitive chromosome count. Genetic counseling before and after testing can help you understand what the numbers actually mean for your specific pregnancy.