Down syndrome

What is Down syndrome? 

Down syndrome (also called trisomy 21) is the most common chromosomal condition in the United States. A chromosomal condition (also called genetic condition) happens when there’s a problem in one or more chromosomes. Chromosomes are the structures that hold genes. Genes are part of your body’s cells that store instructions for the way your body grows and works. Genes are passed from parents to children.

About 1 in 700 babies (less than 1 percent) is born with Down syndrome. Many children with Down syndrome lead healthy, active lives. They can go to school, participate in activities and enjoy being social with others. A person with Down syndrome may live 60 years or more.

What causes Down syndrome?

Each person has 23 pairs of chromosomes, or 46 in all. For each pair, you get one chromosome from your mother and one from your father. Babies with Down syndrome have an extra copy of chromosome 21. This extra copy changes the way the brain and body develop.

We don’t know for sure why Down syndrome happens. It may be that the egg or sperm that come together in fertilization has an extra chromosome. Fertilization is when a man’s sperm gets inside of a woman’s egg. This is how a woman gets pregnant.

These things can affect your risk of having a baby with Down syndrome:

Your age when you get pregnant. Your risk of having a baby with Down syndrome increases as you get older, especially if you are age 35 or older.  

Being a carrier of a certain type of Down syndrome. If you or your partner are a carrier of one type of Down syndrome (translocation Down syndrome), you carry (have) a gene change for the condition, but you don’t actually have the condition. You can pass the gene change to your baby, but it’s rare.

Already having a baby with Down syndrome. If you already have a baby with Down syndrome, your risk for having another is higher.

Talk to a genetic counselor to understand your risk of having a baby with Down syndrome. A genetic counselor is a person who is trained to help you understand genes, birth defects and other medical conditions that run in families and how they can affect your health and your baby's health.

What are the different types of Down syndrome?

There are three types of Down syndrome:

1. Trisomy 21. This is the most common kind. About 95 in 100 people with Down syndrome (95 percent) have trisomy 21. In this condition, your baby’s cells have three copies of chromosome 21 instead of two.  
2. Translocation Down syndrome. About 3 in 100 people with Down syndrome (3 percent) have translocation Down syndrome. This condition happens when a person has two copies of chromosome 21, but they also have an extra part of chromosome 21 or a whole extra chromosome 21 that’s attached (also called translocated) to a different chromosome. Translocation Down syndrome can be inherited (passed from parent to child through genes).
3. Mosaic Down syndrome. About 2 in 100 people with Down syndrome (2 percent) have mosaic Down syndrome. People with this condition have some cells with three copies of chromosome 21, but other cells have the usual two copies. People with mosaic Down syndrome may have fewer characteristics of Down syndrome because they have some cells with the two copies of chromosome 21.

Can you find out during pregnancy if your baby has Down syndrome?

Yes. Health care providers offer testing for Down syndrome to all pregnant women as part of regular prenatal care (medical care you get during pregnancy). You can decide if you want to have these tests. Talk to your health care provider or a genetic counselor about testing for Down syndrome.  

If you or your partner has a family history of Down syndrome, tell your health care provider or genetic counselor. Family history means that someone in either of your families has the condition. Use our family health history form to help you find out if certain health conditions run in your families.

There are two kinds of prenatal tests to check for Down syndrome:

1. Screening tests. These are medical tests to see if you’re at risk or your baby is at risk for certain health conditions. A screening test for Down syndrome checks to see if your baby is more likely than other babies to have Down syndrome. Screening tests are safe for you and your baby, but they don’t tell you for sure if your baby has a condition like Down syndrome.
2. Diagnostic tests. These are medical tests to see if you do or don’t have a certain health condition. Diagnostic tests may have more risks than screening tests, but they can tell you for sure if your baby does or doesn’t have Down syndrome. If a screening test shows your baby is at high risk of Down syndrome, your provider may recommend a diagnostic test to confirm the results.

Screening test results can help you decide if you want to have a diagnostic test. It is your choice whether or not you want to have diagnostic tests. You may or may not want to know for sure during pregnancy if your baby has Down syndrome. If you do find out for sure, you can learn about the condition so you’re prepared when your baby’s born. You also can make plans for the medical care your baby may need.

What screening tests are used for Down syndrome?

Screening tests for Down syndrome include:

• First trimester screening. Your provider uses these tests to see if your baby may be at risk for Down syndrome and certain other birth defects. The test is usually done at 10 to 13 weeks of pregnancy. It has two parts:

1. Blood test. This measures the levels of two proteins in your blood: plasma protein-A (also called PAPP-A) and a pregnancy hormone called human chorionic gonadotropin (also called HCG). If these levels are too high or too low, your baby may be at higher risk for Down syndrome.  
2. Nuchal translucency test. This is an ultrasound to look for extra fluid at the back of your baby’s neck. An ultrasound uses sound waves and a computer screen to show a picture of your baby inside the womb. Extra fluid may mean a higher risk for Down syndrome.

• Second trimester screening. You get a maternal blood test (also called quad screen) to measure up to four substances in your blood that may show a higher risk for Down syndrome: alpha-fetoprotein (AFP), estriol, HCG and inhibin A. A test measuring three of these proteins is called a triple screen, and a test measuring four of these proteins is called a quad screen. The test is usually done at 15 to 22 weeks of pregnancy.
• Integrated screening test. Your provider combines the results from the first trimester screening and the second trimester screening to better estimate the chances that your baby may have Down syndrome.
• Cell-free DNA testing (also called noninvasive prenatal screening or testing or NIPT). This test checks your blood for your baby’s DNA to see if he is at higher risk for Down syndrome. You can have this test as early as 10 weeks of pregnancy. Talk to your provider about whether this test is right for you.

What diagnostic tests are used for Down syndrome?

During a diagnostic test, your provider uses a needle to take a sample of your baby’s blood, amniotic fluid or tissue for testing. There is a small risk of miscarriage with these diagnostic tests. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.

Diagnostic tests for Down syndrome include:

• Chorionic villus sampling (also called CVS). This test checks tissue from the placenta to see if your baby has a genetic condition, like Down syndrome. You can get CVS at 10 to 13 weeks of pregnancy.
• Amniocentesis (also called amnio). This test takes some amniotic fluid from around your baby in the uterus (womb) to check for birth defects and genetic conditions in your baby. You can get this test at 15 to 20 weeks of pregnancy.
• Percutaneous umbilical cord sampling (also called PUBS or cordocentesis). This test takes a small amount of your baby’s blood from the umbilical cord to check for chromosome defects. You can get this test between 18 and 22 weeks of pregnancy. There are greater risks with PUBS than with amnio or CVS, so you only get this test if other tests are unclear and you want to confirm whether or not your baby has Down syndrome.

How are babies with Down syndrome diagnosed after birth?

After birth, your baby’s provider gives your baby a physical exam and checks for common physical characteristics of Down syndrome. To confirm your baby has Down syndrome, she sends a sample of your baby’s blood to a lab for testing.

What are some physical characteristics of a person with Down syndrome?

A person with Down syndrome may have distinct physical characteristics, including:

Facial features. Most babies with Down syndrome have some of these characteristics:

• A flattened face, with a flat nose
• Almond-shaped eyes that slant up
• A small mouth
• A tongue that may stick out of the mouth
• Tiny white spots on the iris (colored part) of the eye

Other physical characteristics. Babies and children with Down syndrome may have some of these characteristics:

• A short neck
• Small hands and feet. They also may have small pinky fingers that sometimes curve towards the thumb.
• A single line across the center of the palm of the hand (also called a palmar crease)
• Small ears 
• Low muscle tone (also called hypotonia) or loose joints
• Short height

How does Down syndrome affect your child’s health and development?

Many people with Down syndrome are healthy, but some need special medical care. Common health and development problems in people with Down syndrome include:

• Intellectual and developmental disabilities. These are problems with how the brain works that can cause a person to have trouble or delays in physical development, learning, communicating, taking care of himself or getting along with others. Babies with Down syndrome may reach developmental milestones later than other babies. A developmental milestone is a skill or activity that most children can do at a certain age. Milestones include sitting, walking, talking, having social skills and having thinking skills. Getting early intervention services as soon as possible can help improve your baby’s development as she grows. These services can help children from birth through 3 learn important skills. Services include therapy to help a child talk, walk, learn self-help skills and interact with others. Visit the Early Childhood Technical Assistance Center to find your state’s contact information for early intervention services.
• Congenital heart defects. These are heart conditions that a baby’s born with. These conditions can affect the heart’s shape or how it works, or both. About half of babies with Down syndrome have congenital heart defects. Like all babies, babies with Down syndrome get heart screening as part of newborn screening tests before they leave the hospital after birth. Babies with Down syndrome also get checked by a pediatric cardiologist, a doctor who treats babies and children with heart problems. If your baby has a congenital heart defect, treatment may include taking medicines or having heart surgery. Sometimes mild heart defects don’t need treatment.
• Hearing loss. Hearing loss can happen when any part of the ear isn’t working in the usual way. It can range from mild to profound (when you can’t hear any speech sounds). About 3 in 4 babies with Down syndrome (75 percent) have hearing loss. Like all babies, babies with Down syndrome get screened for hearing loss as part of newborn screening. Babies with Down syndrome need regular hearing tests. Your baby may need to see an ear, nose and throat (also called ENT) doctor who specializes in treating babies and children (called a pediatric ENT). Babies and children with Down syndrome also may have many ear infections, which can sometimes lead to hearing loss. Your baby may need ear tubes to treat ear infections that won’t go away with medicine. Ear tubes are tiny tubes placed through the ear drum to allow air into the middle ear and prevent fluids from building up behind the ear drum.
• Sleep disorders, like obstructive sleep apnea. Obstructive sleep apnea is when your child’s breathing stops and starts during sleep because her airway becomes narrow or blocked. About 1 in 2 (50 percent) to 3 in 4 babies with Down syndrome (75 percent) have obstructive sleep apnea. Snoring is the most common sign of obstructive sleep apnea. All children with Down syndrome should be checked for obstructive sleep apnea, even if they don’t snore. This can be done during an overnight sleep study in a special sleep lab to check for sleep problems. Your child wears sensors, and a team of health care providers checks your child’s breathing, blood oxygen levels, heart rate and brain waves while she sleeps. Treatment for sleep disorders may include wearing a special mask to help your child breathe during sleep. Sometimes obstructive sleep apnea happens when a child’s tonsils and adenoids are too big. Tonsils and adenoids are lymph tissues near the throat that help protect the body from infection. Your child may need surgery to remove his tonsils and adenoids.
• Vision problems. More than half of children with Down syndrome have vision problems. Some children with Down syndrome have cataracts. This is when the lens of the eye is cloudy instead of clear, making it hard to see. An eye doctor called a pediatric ophthalmologist checks your baby’s vision after birth. Children with Down syndrome need regular eye exams. They may need glasses, surgery or other treatments to help improve their vision.

Some children with Down syndrome have other conditions, including:

• Blood disorders. Your baby gets regular blood tests to check for problems, like low iron or anemia. Anemia is when you don’t have enough healthy red blood cells to carry oxygen to the rest of your body. It’s rare, but some children with Down syndrome may develop a blood cancer called leukemia. These children are treated by a pediatric hematologist-oncologist, a doctor who treats children with blood disorders and cancer. They may need chemotherapy (medicines used to treat cancer).
• Dental problems. Your baby may develop teeth more slowly, in a different order or have fewer teeth than other children. Health care providers recommend that babies with Down syndrome get checked by a dentist within 6 months of getting their first tooth or by age 1.
• Infections. Babies with Down syndrome tend to get sick often because their bodies have trouble fighting off infections. Make sure your baby gets all of her vaccinations on time. Vaccinations help protect your baby from certain diseases. 
• Low muscle tone. Babies with low muscle tone may have trouble with sucking, feeding, swallowing and having bowel movements. If your baby has poor muscle tone, she may have delays in meeting developmental milestones, like rolling over, sitting up, crawling and walking.
• Problems with digestion and the intestines, like Hirschsprung disease. The intestines are long tubes that are part of your digestive system. Your digestive system helps your body break down food, take in nutrients and remove waste. Hirschsprung disease happens when the large intestine (also called the colon) is blocked. Babies with Hirschsprung disease need surgery to remove part of colon that isn’t working well.
• Neck or spine problems. Bones in the neck or spine can be unstable and increase your child’s risk of spinal cord injury. Some children need surgery.
• Hip problems. Children with Down syndrome may be at higher risk for hip dislocation. This is when the thigh bone slips out of place at the hip.
• Thyroid problems. The thyroid is a gland in your neck that makes hormones (chemicals) that help your body store and use energy from food. Babies with Down syndrome may have hypothyroidism. This is when the thyroid gland doesn’t make enough thyroid hormone. If not treated, this can affect your baby’s growth and development. Your baby gets checked for thyroid problems as part of newborn screening and has follow-up tests every year. Thyroid problems are treated with medicine.
• Epilepsy. Children with Down syndrome are more likely to have epilepsy. This is a seizure disorder that affects how the nerve cells in your brain work. A seizure is sudden, abnormal electrical activity in the brain that can cause changes in behavior, movement, feelings and consciousness. Seizures are treated with medicine.
• Mental health and emotional problems. Children with Down syndrome may have behavioral and emotional problems like anxiety, depression and attention deficit hyperactivity disorder (also called ADHD). Children with ADHD may have trouble paying attention and controlling behaviors or be overly active. Treatment may include care from a mental health professional. This is a person with training and education to help people with emotional or mental health problems.
• Microcephaly. This is a birth defect in which a baby’s head is smaller than expected, compared to babies of the same sex and age. Some babies with microcephaly have smaller brains that may not develop properly. To diagnose microcephaly if your baby has Down syndrome, your baby’s provider measures your baby’s head circumference and compares it to other babies’ head measurements. Head circumference is the distance around the top of your baby’s head.

More information

• Linda Crnic Institute for Down Syndrome
• National Down Syndrome Congress
• National Down Syndrome Society 
• National Society of Genetic Counselors

Last reviewed: February 2020