NT Scan vs Double Marker Test: Timing, Differences, Results & How They Work Together
By Dr. Charmi Shah +2 more
Medically reviewed by Dr. Charmi Shah
Last updated: Apr 9, 2026 Published on: Apr 9, 2026
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By Dr. Charmi Shah +2 more
Table of Contents
During early pregnancy, women undergo several screening tests to monitor the baby’s growth and development and detect potential abnormalities, making it an important stage of care1. Among these, the most commonly advised tests include the nuchal translucency (NT) scan and the double marker test. Both play an important role in the early weeks of pregnancy (first trimester)2,3.
These tests help evaluate the risks of genetic disorders like Down syndrome in babies by combining the scanning reports with certain biochemical markers (measurable biological molecules) in the mother’s body2,3.
This article might help you better understand what the NT scan and the double marker test are, their differences, and how they are helpful together to provide a more comprehensive risk assessment during early pregnancy.
An NT scan is a specialised ultrasound performed during the first trimester of pregnancy, usually between 11 to 13weeks + 6days3. It is done to measure the thickness of the nuchal fold (fluid-filled space) on the back of the baby’s neck. This measurement is known as nuchal translucency2.
This test helps assess the risk of several genetic abnormalities, growth or developmental problems, and structural heart disease in babies. In these conditions, greater fluid tends to accumulate in the nuchal space. Thus, an increase in fluid, shown as increased thickness of the nuchal space, might indicate a higher risk of these conditions. However, it does not confirm a problem as it is just a screening (not diagnostic) test. Also, there might be differences in the values based on laboratories, and the result is usually combined with other tests to estimate the risk2.
The double marker test is a screening blood test done during the first trimester, normally between 10 to 13 weeks + 6 days of pregnancy4, ideally along with the NT scan. It measures the levels of two components in the mother’s blood, free beta-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A), a hormone and a protein secreted by the placenta (the tissue that connects the mother to the baby) that helps in the proper functioning of the placenta and normal development of the baby5,6.
This test helps assess the risk of certain genetic abnormalities, such as Down syndrome, Patau syndrome and Edward Syndrome3. The test measures the changes in β-hCG and PAPP-A, which may reflect how the placenta and the baby are developing5. The results are then combined with other factors like the mother’s age and NT test result to estimate overall risk, rather than being looked at separately. However, it might need further diagnostic tests for confirmation3.
The following shows the difference between the NT scan and the double marker test.
| Feature | NT Scan | Double Marker Test |
| Type of test | Ultrasound (Imaging)2 | Blood test (Laboratory)3 |
| Procedure | Non-invasive (surface test without inserting any instruments into the body)2 | Simple blood collection3 |
| What it measures | Thickness of the skin fold behind the baby’s neck2 | Levels of PAPP-A and free-hCG3 |
| Interpretation | Based on gestational age using percentiles7 | MoM (Multiple of Median- compares your values to the average for your pregnancy stage)3 |
| Purpose | Assess structural (congenital heart disease) and genetic abnormalities (e.g. Down syndrome)2 | Assess the risk of genetic disorders such as Down syndrome, Edward syndrome, etc3. |
You might have understood what NT scan and double marker test are. But do you know that they might give more accurate results when combined rather than performed individually?
Yes, the NT scan and the double marker test are used together in early pregnancy to check the baby’s health more accurately8. While the NT scan assesses physical changes by measuring the skin fold or fluid-filled space behind baby’s neck, the double marker test evaluates wo biochemical components in the mother’s blood to estimate the risk of genetic conditions and structural issues. The results from both tests are combined using a reliable risk algorithm that include mother’s age, NT report, and serum markers to give one overall risk score2,3.
As the combined results of these tests may give a more accurate picture than alone, it might help your doctor estimate the chances of certain chromosome-related conditions like Down syndrome. If the risks look too high, the doctor may suggest further testing for confirmation3,8.
Both the NT scan and the double marker test are done during the first trimester, usually between 10 and 14 weeks.
The NT scan and double marker test are two of the most important tests performed during the pregnancy period to detect chromosomal conditions, such as Down syndrome and other genetic and structural abnormalities. These tests, when used together, might increase the accuracy of assessment rather than when tested alone. Doctors can evaluate single and combined risk scores by combining ultrasound outcomes from the NT scan and biochemical results from the double marker test. Based on these results, they can assess whether further tests are required, which might help ensure timely and proper care during early pregnancy.
The NT scan and double marker test are performed between 11 and 14 weeks, as testing combining them might give more accurate results rather than being done alone3,8. Therefore, it might be good enough to perform these tests on the same day, which might make the procedure less hectic for the mother and might make it easy to correlate the results.
The double marker test is usually performed between 10 and 13 weeks+ 6 days of pregnancy4, which means between the 3rd and 4th months.
NT scan and double marker tests may not confirm a baby’s genetic conditions, as they are only screening tests. They only evaluate the risk of a baby having a genetic disorder. To confirm the genetic condition, the doctors perform prenatal diagnostic testing, such as chorionic villus sampling or amniocentesis4.
If both the results show different risk values, then they may not be interpreted by the doctor separately. Instead, both results may be combined to calculate a single overall risk score for conditions. If the combined result is low risk, the pregnancy is usually considered normal, and if it is high, further tests may be recommended. However, these aren’t diagnostic tests but just screening tests. Further diagnostic tests such as amniocentesis may be performed to confirm the abnormalities if risk is high in these4,8.
These tests are usually considered safe for both mother and the baby, as they include non-radiation imaging and a simple blood collection procedure. However, sometimes the double marker test can cause small, possibly rare side effects like bruising, bleeding, or localised pain that may occur in the mother after blood collection4.
1. Healthdirect Australia. Routine antenatal tests [Internet]. Canberra: Healthdirect Australia; [cited 2026 Apr 9]. Available from: https://www.healthdirect.gov.au/routine-antenatal-tests
2. MedlinePlus. Nuchal translucency test [Internet]. Bethesda (MD): U.S. National Library of Medicine; [cited 2026 Apr 9]. Available from: https://medlineplus.gov/ency/article/007561.htm
3. Shiefa S, Amargandhi M, Bhupendra J, Moulali S, Kristine T. First Trimester Maternal Serum Screening Using Biochemical Markers PAPP-A and Free β-hCG for Down Syndrome, Patau Syndrome and Edward Syndrome. Ind J Clin Biochem. 2013;28(1):3-12. doi:10.1007/s12291-012-0269-9. Available from: https://pubmed.ncbi.nlm.nih.gov/24381414/
4. Maines J, Langaker MD. Prenatal genetic screening [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan– [updated 2025 Apr 18; cited 2026 Apr 9]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557702/
5. Ogino MH, Tadi P. Physiology, Chorionic Gonadotropin. In: StatPearls. StatPearls Publishing; 2026. Accessed March 31, 2026. Available from: http://www.ncbi.nlm.nih.gov/books/NBK556118/
6. Papamichail M, Fasoulakis Z, Daskalakis G, Theodora M, Rodolakis A, Antsaklis P. Importance of Low Pregnancy Associated Plasma Protein-A (PAPP-A) Levels During the First Trimester as a Predicting Factor for Adverse Pregnancy Outcomes: A Prospective Cohort Study of 2636 Pregnant Women. Cureus. 14(11):e31256. doi:10.7759/cureus. 31256. Available from: https://pubmed.ncbi.nlm.nih.gov/36505175/
7. Kaul A, Radhakrishnan P. Performance of Common Down Syndrome Screening Methods Used in India with Construction of an Indian Normogram for Nuchal Translucency/Crown–Rump Length Measurements in 14,337 Subjects. J Obstet Gynecol India. 2019;69(S2):142-146. doi:10.1007/s13224-018-1196-3. Available from: https://pubmed.ncbi.nlm.nih.gov/31686747/
8. Heidari R, Akbariqomi M, Motevaseli E, et al. Performance and Predictive Value of First Trimester Screening Markers for Down Syndrome in Iranian Pregnancies. J Family Reprod Health. 2018;12(3):121-128. Available from: https://pubmed.ncbi.nlm.nih.gov/31223317/
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