Babies with Down syndrome have an extra copy of chromosome 21, which changes how the brain and body develop.
People with Down syndrome may have physical problems, learning problems and distinct physical features.
Many people with Down syndrome are healthy, but some need medical care for birth defects or other health conditions.
Talk to your health care provider or a genetic counselor to learn about testing for 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 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.
About 1 in 700 babies (less than 1 percent) is born with Down syndrome. Many children with Down syndrome lead healthy, active lives. They go to school, play sports 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 in every cell in their body. For each pair, you get one chromosome from your mother and one chromosome 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 a woman’s egg to make her pregnant. One kind of Down syndrome (called translocation Down syndrome) can be passed from a parent to a child, but it’s rare.
Your age when you get pregnant affects your risk of having a baby with Down syndrome. The older you are, the higher your risk. If you get pregnant:
- At age 25, your risk of having a baby with Down syndrome is 1 in 1,340.
- At age 30, your risk is 1 in 940.
- At age 35, your risk is 1 in 353.
- At age 40, your risk is 1 in 85.
- At age 45, your risk is 1 in 35.
If you already have a baby with Down syndrome, your risk for having another increases with each pregnancy. Up to age 40, for each pregnancy your chances of having another baby with Down syndrome is about 1 in 100 (1 percent). After age 40, the risk is based your age. Talk to a genetic counselor to understand your risk. A genetic counselor is a person who is trained to help you understand about 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 kinds of Down syndrome?
There are three kinds of Down syndrome:
- 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.
- Mosaic Down syndrome. People with this condition have some cells with three copies of chromosome 21, but other cells have the usual two copies. Mosaic Down syndrome is rare. People with Mosaic Down syndrome may have fewer characteristics of Down syndrome because they have some cells with the two copies of chromosome 21.
- Translocation Down syndrome. This condition happens when a person has two copies of chromosome 21, plus an extra part of a chromosome or a whole extra chromosome that’s attached (also called translocated) to one copy of chromosome 21. This condition is rare, and it can be inherited (passed from parent to child).
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 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:
- Screening tests. These tests check if your baby is more likely than others to have Down syndrome. There are no risks to you or your baby when you have a screening test, but they don’t tell you for sure if your baby has a condition like Down syndrome.
- Diagnostic tests. These tests 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.
Each kind of test has pros and cons. Screening test results can help you decide if you want to have a diagnostic test. 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 to give birth in a hospital that can give your baby special medical care.
What screening tests are used for Down syndrome?
Screening tests are called noninvasive because your provider doesn’t need to use tools that break your skin or enter your body. Instead, you get a blood test or an ultrasound. Ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb.
Screening tests for Down syndrome include:
- First trimester screening (also called first trimester combined test). Your provider uses these test results and your age to estimate your chances of having a baby with Down syndrome. This test is usually done at 11 to 14 weeks of pregnancy. It has two parts:
- Blood test. This measures levels of plasma protein-A (also called PAPP-A) and a pregnancy hormone called human chorionic gonadotropin (also called HCG) in your blood. If your PAPP-A and HCG levels aren’t normal, your baby may have Down syndrome.
- Nuchal translucency test. Your provider uses this special kind of ultrasound to measure the tissue at the back of your baby’s neck (called the nuchal fold). Extra fluid in the nuchal fold may be a sign that your baby may have Down syndrome.
- Integrated screening test. Your provider uses these two tests to estimate the chances that your baby has Down syndrome:
- First trimester. You get a blood test to check your PAPP-A levels and an ultrasound to measure your baby’s nuchal fold. This test is usually done at 11 to 14 weeks of pregnancy.
- Second trimester. You get a maternal blood test (also called quad screen) to measure four substances in your blood: alpha-fetoprotein (AFP), estriol, HCG and inhibin A. The test is usually done at 15 to 22 weeks of pregnancy.
- 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 may have Down syndrome. You can have this test as early as 10 weeks of pregnancy. If you’re at high risk of having a baby with Down syndrome, your provider may recommend this test. It’s not recommended if you aren't likely to have a baby with a birth defect or if you’re pregnant with multiples (more than one baby, like twins or triplets).
What diagnostic tests are used for Down syndrome?
If a diagnostic test for Down syndrome is positive, it means your baby has the condition. If it’s negative, your baby doesn’t have Down syndrome. Diagnostic tests are called invasive because your provider uses a needle to take a sample of your baby’s blood, amniotic fluid or tissue for testing. There is a risk of miscarriage with diagnostic tests. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.
Diagnostic tests for Down syndrome include:
- Amniocentesis (also called amnio). This test takes some amniotic fluid from around your baby in the uterus (also called womb) to check for Down syndrome. You can get an amnio at 15 to 20 weeks of pregnancy.
- Chorionic villus sampling (also called CVS). This test checks tissue from the placenta to see if a baby has Down syndrome. You can get CVS at 10 to 13 weeks of pregnancy.
- Cordocentesis (also called percutaneous umbilical cord sampling or PUBS). Your provider inserts a thin needle into an umbilical cord vein to take a small sample of your baby’s blood to check for chromosome defects. You can get this test between 18 and 22 weeks of pregnancy. There’s a much greater risk of miscarriage with cordocentesis than with amnio or CVS, so you only get this test if other tests are unclear and your provider can’t confirm your baby has Down syndrome any other way.
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, but not all 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 a single line across the center of the palm of the hand (also called a palmar crease) or small pinky fingers that curve towards the thumb.
- Small ears that may fold over a little at the top
- Low muscle tone (also called hypotonia) or loose joints. Babies with Down syndrome have low muscle tone at birth. They may seem floppy and have poor head control.
- Short height
How does Down syndrome affect your child’s health and development?
Most people with Down syndrome are healthy, but some need special medical care. Common health and development problems in people with Down syndrome include:
- Congenital heart defects. These are heart conditions a baby’s born with that 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.
- Hearing loss. This is when your baby can’t hear sound in one or both ears. 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. Your baby also needs follow-up hearing tests every 6 months and may need to see an ear, nose and throat (also called ENT) doctor who specializes in treating babies and children (called a pediatric ENT). Your baby may need ear tubes. These 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.
- 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. The services can help children from birth through 3 years learn important skills, like how to talk, walk and interact with others. To find out about early intervention services in your state, visit the Early Childhood Technical Assistance Center.
- 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. Snoring is the most common sign of obstructive sleep apnea. Children with sleep apnea often have larger tonsils and adenoids than other children. Tonsils and adenoids are lymph tissues near the throat that help protect the body from infection. All children with Down syndrome should be checked for obstructive sleep apnea during an overnight sleep study in a hospital before they’re 4 years old. Your child wears sensors, and a team of health care providers checks your child’s breathing, blood oxygen levels and brain waves while she sleeps. Treatment for sleep disorders may include wearing a mask to help your child breathe during sleep or surgery to remove your child’s tonsils and adenoids.
- Vision problems. More than half of children with Down syndrome have vision problems. An eye doctor called a pediatric ophthalmologist checks your baby’s vision at birth and at 1 year. Children with Down syndrome need regular eye exams. She may need glasses, surgery or other treatments to help improve her vision.
Some children with Down syndrome have other conditions, including:
- Blood disorders. Your baby gets yearly 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 have 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.
- 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.
- 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 with Down syndrome who have microcephaly. Head circumference is the distance around your baby’s head.
- Low muscle tone. Babies with low muscle tone may have trouble with sucking, feeding, weight gain and 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 the intestines, like Hirschsprung disease. The intestines are long tubes that are part of your body’s 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 Hisrchsprung 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.
- Thyroid problems. The thyroid is a gland in your neck that makes hormones (chemicals) that help the body use and store energy. Babies with Down syndrome may have low thyroid hormone levels. 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.
Last reviewed: October, 2016