Feb 28, 2023 • 8 min read

Can You Tell if Your Baby Has Down Syndrome from an Ultrasound?

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With today’s modern advances in medical care, there are now several tests and other tools to give parents insight into how their new baby is developing. There are several tests that can be done to assess the likelihood of a baby having Down syndrome.

Ultrasound is one method to detect Down syndrome and is typically minimally invasive.

The decision to have a prenatal screening test is up to you and they are not mandatory. It is a decision to make based on your desires, beliefs, and values. Everyone is different and chooses what is best for their family.

Some people decide not to do any screening tests. Some decide to do screening tests but no diagnostic tests, even if there is a risk marker shown on the screening. There is no right or wrong decision because every case is different.

This guide will go over everything you need to know about if ultrasounds can detect Down syndrome, other tests, timelines for screening, and more.

Can ultrasound detect Down syndrome?

Ultrasound is a valuable and noninvasive tool that can be used to assess the risk and likelihood of a baby having Down syndrome. It is great at visualizing anatomical features associated with Down syndrome.

If you opt for the basic prenatal blood work/screening tests and things come back normal or something comes back abnormal, ultrasound is used to decide if you need more diagnostic testing to definitively confirm whether or not your baby has Down syndrome.

What is Down syndrome?

Down syndrome (Trisomy 21) is the most common syndrome observed in humans with an overall incidence of approximately 1 in 500 to 700 newborns.

Trisomy is a medical term for having an extra copy of a chromosome. Normally, babies are born with 46 chromosomes. Babies with Down syndrome are born with an extra copy of Chromosome 21 (Trisomy 21). This extra copy affects how a baby’s brain and body develop.

This condition can cause physical and neurological problems for the baby. Each person with Down syndrome is different and may have milder or more severe difficulties.

What does ultrasound do?

Sonography (Ultrasound) is based on non-ionizing radiation, so it does not have the same risks as X-rays or other imaging systems that use ionizing radiation like CT, CAT, PET scans, Mammograms, and Fluoroscopy.

Instead, with ultrasound, an image is generated through sound waves, frequency, and reflection. Doctors have used ultrasound for decades and it is still one of the safest imaging modalities available.

Ultrasound accurately assesses gestational age, confirms fetal viability, detects multiples in pregnancy (including the number of placentas and amniotic sacs), locates placenta positioning, and diagnoses intrauterine growth restriction and fetal anomalies. It is also used in guidance for Chorionic Villus Sampling (CVS), Amniocentesis, and Percutaneous Umbilical Blood Sampling (PUBS).

Sonography provides parents with information necessary to make informed decisions about the pregnancy.

How can ultrasound be used to screen for Down syndrome?

Ultrasound is used as a screening test that can be done in the first and/or second trimester. Visual characteristics that may indicate potential Down syndrome in ultrasound include:

  • Thickened nuchal translucency
  • Underossified or unossified nasal bone
  • Shortened femur and/or humerus
  • Dilated of the kidney(s)
  • Echogenic bowel
  • Heart defects

When is ultrasound used to detect Down syndrome?

In weeks 9 to 13 of the first trimester, ultrasound is used to evaluate nuchal translucency. This ultrasound measures a specific area behind the baby’s neck. If the measurement of fluid behind the neck is over the normal range, there may be abnormalities present.

Nasal bone measurement and ductus venous flow can also be used to increase sensitivity in first-trimester screenings.

In the second trimester (14 to 28 weeks), approximately 30% of babies with Down syndrome have noticeable abnormalities visualized on ultrasound. These soft markers are seen more frequently in babies with abnormalities:

  • Mildly shortened femur and/or humerus
  • Mild fetal pyelectasis (dilation of one or both kidneys)
  • Echogenic bowel (bright areas seen on ultrasound within the bowel)
  • Hypoplasia of the middle phalanx of the fifth digit
  • Brachycephaly (shortened measurement of the head)
  • Echogenic intracardiac focus (bright spot in the left ventricle of the heart, at the level of the papillary muscle)
  • Under ossified nasal bones (in 70-80% of first and second-trimester fetuses with Down syndrome, the nasal bone is unossified or underossified)
  • Heart defects (numerous cardiac defects have been observed in Down syndrome, the most common being atrioventricular canal defects)

How accurate/definitive is an ultrasound screening in predicting Down syndrome?

There is a Sonographic Scoring system for Fetal Anomalies Associated With Chromosomal Abnormality. Bernaceraf et al. in 1994 proposed a scoring system with risk of major chromosomal anomalies in the presence of specific abnormalities.

According to this system, when a baby has a score of 2 or more, it is suggested that the mother should have an amniocentesis. The higher the score, the higher chance of Trisomy 21 being present.

Ultrasound is most accurate when it is used in combination with blood screening tests or other diagnostic tests.

Ultrasound for a baby with Down syndrome vs. a normal baby

One of the characteristics seen on ultrasound that may indicate a baby has Down syndrome is the absence of a nasal bone seen on a side profile view of the baby’s face. Normally you would see a clearly defined nasal bone.

Another characteristic would be a shortened measurement of the baby’s head. In a baby with Down syndrome, you might see a rounder head or a head that is flatter on the back. A normal fetal head shape is slightly more oval-shaped, and measurements correlate with gestational age.

It’s important to note that ultrasound is not absolute and can present normally in all areas, indicating a normal fetus. This is why it’s important to do additional screening tests to assess risk more accurately or diagnostic tests to get a definitive diagnosis.

Other screening tests for Down syndrome

There are several screening tests you can discuss with your healthcare provider. A screening test is just that, it can’t give a guaranteed diagnosis without diagnostic testing. It can, however, tell you the likelihood and risk percentage there is for Down syndrome.

Multiple types of screening tests, in combination, can make those results more accurate.

Blood tests measuring various types of substances in the mother’s blood include:

  • MS-AFP (maternal serum alpha-fetoprotein)
  • Acetylcholinesterase
  • Unconjugated estriol
  • PAPP-A (pregnancy-associated plasma protein-A)
  • HCG (human chorionic gonadotropin)

If these values are not within the normal range, it may indicate there is a problem with the baby.

Diagnostic tests for Down syndrome

Diagnostic tests are usually recommended after one or more screening tests have shown that a baby is at high risk for Down syndrome. It is the final step in getting an accurate diagnosis.

There are multiple diagnostic tests available, and your healthcare provider can let you know which would be most accurate and beneficial based on your baby’s unique cases.

Gestational age, results from screening tests, maternal age, and fetal position are all factors your doctor needs to consider when choosing the best diagnostic option. These diagnostic tests are not mandatory and are always a personal choice.

Diagnostic tests for Down syndrome include:

Chorionic Villus Sampling (CVS)

Chorionic Villus Sampling is used to get a better diagnosis of many genetic disorders in the first trimester. Genetically, the placenta is a fetal organ that contains fetal genetic information.

The sample is taken from the villi along the site of implantation of the placenta. This sampling is done with the assistance of ultrasound to show where that area of implantation is.

Once the location is established, a transcervical or transabdominal approach can be decided. Transcervical means, through the vaginal canal and cervix. Transabdominal means over the pelvis.

The transcervical approach is performed between 10 to 12 weeks. A speculum is inserted and the vagina is cleaned with an antibiotic solution.

Under direct ultrasound visualization, a biopsy catheter is inserted into the developing placenta, a syringe is attached to the catheter, and the catheter tip is moved gently back and forth in the sample site while suction is applied.

After a sample is obtained, it is visualized under a microscope.

The transabdominal approach of chorionic villus sampling is done in cases of an anterior placenta (the placenta is implanted on the front wall of the uterus instead of the back wall, towards your back).

Under direct ultrasound visualization, the physician inserts an 18 to 20-gauge needle into the placenta under aseptic conditions. A syringe is attached to the needle and suction is applied while the needle is gently moved back and forth within the placenta.

This method can be performed at any time in the pregnancy if the placenta is in an anterior location.


Amniocentesis is a procedure where a sample of amniotic fluid is extracted to test for genetic conditions. Amniotic fluid is what surrounds and protects the baby in the womb. This procedure can be done after 15 weeks.

Percutaneous Umbilical Blood Sampling (PUBS)

PUBS, also called Cordocentesis, is the sampling of blood from the umbilical cord vein and is usually done after 18 to 19 weeks.

How these tests are analyzed

There are different technologies available for analyzing diagnostic test results. These are the most common:

  • Karyotyping. Missing, damaged, or extra chromosomes can be detected by taking an image of the sample and arranging them by largest to smallest. These results are ready in 1 to 2 weeks.
  • Fluorescence In Situ Hybridization. This technique is used specifically for Trisomy 13, 18, 21, and the X and Y chromosomes. Results are ready within 2 days.
  • Chromosome Microarray Analysis. This can identify many more chromosome abnormalities and catch some that karyotyping might miss.
  • DNA testing. Tests for specific gene mutations can be done by request.

Options for finding out if your baby has Down syndrome at each stage of pregnancy

It is recommended to offer the option of screening tests and diagnostic testing for Down syndrome to all pregnant women, regardless of age, before 20 weeks.

Screening for Down syndrome is a regular part of prenatal care because of the American College of Obstetricians & Gynecologists’ recommendation. It’s important to remember, screening tests only assess risk, there is still room for false positives.

This is a breakdown of which stages in your pregnancy you can have specific screening/diagnostic testing done:

  • First Trimester: During this time, you may consider these blood screening tests, Nuchal Translucency Ultrasound screening, and the Transcervical CVS diagnostic test (depending on placenta location). Options for testing for Down syndrome in the first trimester include:
    • MS-AFP (maternal serum alpha-fetoprotein)
    • Acetylcholinesterase
    • Unconjugated estriol
    • PAPP-A (pregnancy-associated plasma protein-A)
    • HCG (human chorionic gonadotropin)
  • Second Trimester: During this time, you may consider a detailed ultrasound screening to check for soft markers and the following diagnostic tests:
    • CVS (transcervical or transabdominal, depending on placenta location)
    • Amniocentesis
    • PUBS

How to decide to test or screen for Down syndrome

If your screening tests suggest high risk, there are diagnostic tests you can choose to get a confirmed diagnosis. Some decide to do screening and diagnostic testing.

Some parents decide to go ahead with testing because they want to prepare for any challenges they may face throughout the pregnancy, to learn as much as they can about the condition, to learn their options for continuing or terminating the pregnancy, or for support after their baby is born.

There are also parents who decide to continue their pregnancy even with a confirmed diagnosis.

Lastly, some parents decide not to find out at all due to personal or religious beliefs, or they want to go through the pregnancy without the stress it may cause if they know ahead of time.

Every child with Down syndrome is unique and may or may not require certain treatments or services at different stages of life. It is important to have open communication and discussion with your healthcare provider so they can help point you towards resources available in whichever choice you make.

Jasmine Denos is a mother of 4 with a passion for pregnancy and motherhood. She has over 9 years of experience as a Registered Diagnostic Medical Sonographer and has specialty certifications in Vascular Technology and OB/GYN.