Screening for down syndrome
Prenatal Testing for Down Syndrome | Patient Education
Age-Related Risks
Generally, the chance of having a Down syndrome birth is related to the mother's age. Under age 25, the odds of having a child with Down syndrome are about 1 in 1,400. At age 35, the odds are about 1 in 350. At age 40, the odds are about 1 in 100.
Causes of Down Syndrome
There are three causes of Down syndrome:
Trisomy 21
An estimated 95 percent of people with Down syndrome have trisomy 21, meaning they have three number 21 chromosomes instead of two. We normally have 23 pairs of chromosomes, each made up of genes. During the formation of the egg and the sperm, a woman's or a man's pair of chromosomes normally split so that only one chromosome is in each egg or sperm. In trisomy 21, the 21st chromosome pair does not split and a double dose goes to the egg or sperm. An estimated 95 to 97 percent of the extra chromosome is of maternal origin.
Translocation
Translocation occurs in about 3 to 4 percent of people with Down syndrome. In this type, an extra part of the 21st chromosome gets stuck onto another chromosome. In about half of these situations, one parent carries the extra 21st chromosome material in a "balanced" or hidden form.
Mosaicism
In mosaicism, the person with Down syndrome has an extra 21st chromosome in some of the cells but not all of them. The other cells have the usual pair of 21st chromosomes. About 1 to 2 percent of people with Down syndrome have this type.
Prenatal Testing
Screening tests can identify individuals at increased risk of having a baby with Down syndrome. These tests have no risks of miscarriage, but can't determine with certainty whether a fetus is affected. Diagnostic tests, on the other hand, are extremely accurate at identifying certain abnormalities in the fetus, but carry a small – generally less than 1 percent – risk of miscarriage. We offer options for both screening and diagnostic testing.
Continue reading
Screening Tests
California prenatal screening (CA PNS) – All pregnant individuals in California have access to CA PNS, also called sequential integrated screening.
This noninvasive screening process is performed in two steps.
In the first step, which is performed between 10 and 14 weeks of pregnancy, a blood sample is taken from the mother and a nuchal translucency ultrasound is performed to measure the amount of fluid at the back of the baby's neck. If the blood test is scheduled prior to the ultrasound, we can provide the results at the end of the ultrasound appointment. The results of the blood test, the nuchal translucency measurement and the mother's age are used to estimate the risk for Down syndrome and trisomy 18.
The second step is a maternal blood test between 15 to 20 weeks of pregnancy. When the results of this blood test are combined with the results from the first trimester blood test and nuchal translucency ultrasound, the detection rate for Down syndrome increases. This test also provides a personal risk assessment for having a fetus with trisomy 18, Smith-Lemli-Opitz syndrome, an open neural tube defect or an abdominal wall defect.
Diagnostic Tests
Amniocentesis, chorionic villus sampling (CVS) and ultrasound are the three primary procedures for diagnostic testing.
Amniocentesis. Amniocentesis is used most commonly to identify chromosomal problems such as Down syndrome. When the fetus is known to be at risk, it can detect other genetic diseases like cystic fibrosis, Tay-Sachs disease and sickle cell disease.
An amniocentesis procedure for genetic testing is typically performed between 15 and 20 weeks of pregnancy. Under ultrasound guidance, a needle is inserted through the abdomen to remove a small amount of amniotic fluid. The cells from the fluid are then cultured and a karyotype analysis – an analysis of the chromosomal make-up of the cells – is performed. It takes about two weeks to receive the results of the test.
Amniocentesis detects most chromosomal disorders, such as Down syndrome, with a high degree of accuracy. Testing for other genetic diseases, such as Tay-Sachs disease, is not routinely performed but can be detected through specialized testing if your fetus is known to be at risk.
Testing for neural tube defects, such as spina bifida, also can be performed.
There is a small risk of miscarriage as a result of amniocentesis – about 1 in 100 or less. Miscarriage rates for procedures performed at UCSF Medical Center are less than 1 in 350.
Chorionic Villus Sampling (CVS). Like amniocentesis, chorionic villus sampling is used most commonly to identify chromosomal problems such as Down syndrome. It can detect other genetic diseases like cystic fibrosis, Tay-Sachs disease and sickle cell disease in at-risk fetuses. The main advantage of CVS over amniocentesis is that it is done much earlier in pregnancy, at 10 to 12 weeks rather than 15 to 20 weeks.
CVS involves removing a tiny piece of tissue from the placenta. Under ultrasound guidance, the tissue is obtained either with a needle inserted through the abdomen or a catheter inserted through the cervix. The tissue is then cultured and a karyotype analysis of the chromosomal make-up of the cells is performed.
It takes about two weeks to receive the results.
The advantage of CVS over amniocentesis is that the test is performed much earlier in pregnancy, so results are typically available by the end of the third month. A disadvantage is that spinal cord defects cannot be detected. Expanded alpha fetoprotein (AFP) blood testing or ultrasound can be performed later in the pregnancy to screen for spinal cord defects.
There is a small risk of miscarriage as a result of CVS – 1 in 100 or less. Miscarriage rates for procedures performed at UCSF Medical Center are less than 1 in 350.
Ultrasound. The primary purpose of ultrasound is to determine the status of a pregnancy – the due date, size of the fetus and if the mother is carrying multiples. Ultrasound also can provide some information about possible birth defects in a fetus. All patients at UCSF Medical Center undergo a comprehensive ultrasound examination before any invasive tests are performed. Results of the ultrasound are explained at the time of the visit.
In some patients, an ultrasound raises concern of a possible abnormality in the fetus. We have extensive experience in performing and interpreting ultrasounds in pregnancy.
If You Receive a Positive Result
If you receive positive results on a screening test, we recommend that you discuss this with your doctor and a genetic counselor. Options for further diagnostic testing will be explained. The decision as to whether to have invasive genetic testing is up to you.
If a diagnostic test finds a genetic abnormality, the significance of such results should be discussed with experts familiar with the condition, including a medical geneticist and a genetic counselor, as well as your own doctor.
UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.
Related clinic
Prenatal Diagnostic Center
1825 Fourth St., Third Floor
San Francisco, CA 94158
(415) 476-4080
M-F, 8 a.m. - 5 p.m.
Screening for Down syndrome | Pregnancy Birth and Baby
Screening for Down syndrome | Pregnancy Birth and Baby beginning of content5-minute read
Listen
If you or someone you care about has a child with Down syndrome, or is pregnant with a Down syndrome baby, you may have many questions or feel overwhelmed by what this means. The most important thing that babies with Down syndrome need — just like any baby — is a loving, secure environment in which they feel nurtured and supported.
What is Down syndrome?
Down syndrome is the most common chromosomal condition that a baby can be born with.
Around 1 in every 1,000 babies born in Australia has Down syndrome.
Down syndrome is also known as Trisomy 21. People with Down syndrome usually look different from other people and may have some difficulty learning new things.
What causes Down syndrome?
Normally, every cell in the human body — except egg and sperm cells — has 46 chromosomes. The egg and sperm cells normally have 23 chromosomes each.
The most common cause of Down syndrome is when an extra copy of chromosome 21 randomly appears in either the egg or sperm. At conception, when the egg and sperm meet, the extra copy of chromosome 21 grows throughout all of the embryo’s cells, giving them each 47 chromosomes instead of the usual 46.
Less commonly, the extra copy of the chromosome can appear in some of the embryo’s cells after conception. This is called mosaicism and results in some cells having 46 chromosomes and some having 47.
Another rare form of the syndrome is caused by ‘Robertsonian translocation’.
This occurs when a piece of chromosome 21 breaks off and becomes joined to another chromosome before or after conception. In this case, the embryo’s cells will all have 46 chromosomes, but each cell still contains an extra copy of chromosome 21.
What are the most common features of Down syndrome?
Many babies with Down syndrome have one or more of the following features at birth:
- low muscle tone ('floppy' muscles)
- a flatter face with eyes slanting upward
- small ears and a wider neck than usual
- a single crease across the palm of the hand
- a gap between the first and second toes
Down syndrome is also associated with intellectual disability.
However, not everyone with Down syndrome will have all of these features.
What medical complications might come with Down syndrome?
About 1 in every 2 babies born with Down syndrome will have heart problems and approximately 1 in 10 will have gastrointestinal (gut) problems.
Hearing and vision problems are also more common in people with Down syndrome.
How is Down syndrome diagnosed?
Pregnant women are offered routine antenatal tests at different times during pregnancy and for different reasons. These include screening tests, such as ultrasounds and blood tests, that can help estimate your baby’s risk of being born with a range of conditions, including Down syndrome.
Non-invasive prenatal testing (NIPT) is a new blood test that can be done as an alternative screening test.
Diagnostic tests (such as chorionic villus sampling or amniocentesis) will show whether a baby actually has Down syndrome.
After the baby is born, chromosome testing from a blood sample, may be done to confirm Down syndrome.
What is the treatment for Down syndrome?
There is currently no way to prevent or cure Down syndrome. Prenatal testing allows you and your family to make informed decisions, including ending the pregnancy. For this reason, before you have the test it’s a good idea to think about why you are choosing to do it, and how you will feel once you get the results.
Consider also who you want to discuss any important decisions with — your partner, a friend or family member, or a health professional such as your doctor or midwife are all good options.
Early diagnosis can also help you and your doctor continue to check your baby for complications and to act early if needed. Some people with Down syndrome may need surgery to repair heart defects or gut blockages. Medicines to treat thyroid disease may also be needed in some cases.
Children all learn and develop at their own pace. However, there are effective early intervention programs for children with Down syndrome that can help them reach their learning potential.
Resources and support
Down Syndrome Australia provides support, information and resources for people with Down syndrome and their families across Australia.
Support services include:
- information and advice about Down syndrome
- information about local support groups
- home visits
- new parent packs
- workshops and webinars
- online support groups for you and your family
A national phone number (1300 881 935) can connect you with your local state or territory Down syndrome organisation for further information.
Speak to a maternal child health nurse
Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.
Sources:
Centre for Genetics education (Trisomy 32 - Down Syndrome), Lab Tests Online (Down syndrome), Down Syndrome Australia (Prenatal and New Parent)Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: March 2022
Back To Top
Related pages
- Caring for a child with Down syndrome
- What is Down syndrome?
- Questions to ask your doctor about tests and scans
- Routine antenatal tests
- Pregnancy checkups, screenings and scans
Need more information?
Support - Prenatal Screening
People often contact our service to better understand their screening results
Read more on Prenatal Screening - Down Syndrome Queensland website
Maternal screening - Pathology Tests Explained
Why and when to get tested for maternal screening
Read more on Pathology Tests Explained website
DSA Prenatal Testing Factsheet - Prenatal Screening
Support through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancy
Read more on Prenatal Screening - Down Syndrome Queensland website
Prenatal Screening for Chromosomal and Genetic Conditions
Read more on RANZCOG - Royal Australian and New Zealand College of Obstetricians and Gynaecologists website
Non-invasive prenatal testing (NIPT)
A non-invasive prenatal test (NIPT) is a sensitive test to screen for Down syndrome and some other chromosomal disorders early in pregnancy.
Read more on Pregnancy, Birth & Baby website
What it's like to Receive an Unexpected Result - Prenatal Screening
Support through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancy
Read more on Prenatal Screening - Down Syndrome Queensland website
Dear Doctor, we want you to know... - Prenatal Screening
Support through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancy
Read more on Prenatal Screening - Down Syndrome Queensland website
Maternity Consumer Network Patient Information Brochure - Prenatal Screening
Support through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancy
Read more on Prenatal Screening - Down Syndrome Queensland website
What is Down syndrome?
Down syndrome is a genetic disorder characterised by mental and developmental impairments.
Read more on Pregnancy, Birth & Baby website
What is Down syndrome? – Down Syndrome Australia
Down syndrome is a genetic condition and is also sometimes known as trisomy 21. You can find out more about Down syndrome below. You can also turn on the Easy Read for this page.
Read more on Down Syndrome Australia website
Disclaimer
Pregnancy, Birth and Baby is not responsible for the content and advertising on the external website you are now entering.
OKNeed further advice or guidance from our maternal child health nurses?
1800 882 436
Video call
- Contact us
- About us
- A-Z topics
- Symptom Checker
- Service Finder
- Linking to us
- Information partners
- Terms of use
- Privacy
Pregnancy, Birth and Baby is funded by the Australian Government and operated by Healthdirect Australia.
Pregnancy, Birth and Baby is provided on behalf of the Department of Health
Pregnancy, Birth and Baby’s information and advice are developed and managed within a rigorous clinical governance framework. This website is certified by the Health On The Net (HON) foundation, the standard for trustworthy health information.
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
This information is for your general information and use only and is not intended to be used as medical advice and should not be used to diagnose, treat, cure or prevent any medical condition, nor should it be used for therapeutic purposes.
The information is not a substitute for independent professional advice and should not be used as an alternative to professional health care. If you have a particular medical problem, please consult a healthcare professional.
Except as permitted under the Copyright Act 1968, this publication or any part of it may not be reproduced, altered, adapted, stored and/or distributed in any form or by any means without the prior written permission of Healthdirect Australia.
Support this browser is being discontinued for Pregnancy, Birth and Baby
Support for this browser is being discontinued for this site
- Internet Explorer 11 and lower
We currently support Microsoft Edge, Chrome, Firefox and Safari. For more information, please visit the links below:
- Chrome by Google
- Firefox by Mozilla
- Microsoft Edge
- Safari by Apple
You are welcome to continue browsing this site with this browser. Some features, tools or interaction may not work correctly.
Screening tests for Down syndrome in the first 24 weeks of pregnancy
Relevance
Down's syndrome (also known as Down's disease or Trisomy 21) is an incurable genetic disorder that causes significant physical and mental health problems and disability. However, Down syndrome affects people in completely different ways.
Some have significant symptoms, while others have minor health problems and are able to lead relatively normal lives. There is no way to predict how badly a child might be affected. nine0006
Expectant parents during pregnancy are given the opportunity to have a screening test for Down syndrome in their baby to help them make a decision. If a mother is carrying a child with Down syndrome, then a decision should be made whether to terminate the pregnancy or keep it. The information gives parents the opportunity to plan life with a child with Down syndrome.
The most accurate screening tests for Down syndrome include amniotic fluid (amniocentesis) or placental tissue (chorionic villus biopsy (CVS)) to identify abnormal chromosomes associated with Down syndrome. Both of these tests involve inserting a needle into the mother's abdomen, which is known to increase the risk of miscarriage. Thus, screening tests are not suitable for all pregnant women. Therefore, more often take blood and urine tests of the mother, and also conduct an ultrasound examination of the child.
These screening tests are not perfect because they can miss cases of Down syndrome and are also at high risk of being positive when the child does not have Down syndrome. Thus, if a high risk is identified using these screening tests, further amniocentesis or CVS is required to confirm the diagnosis of Down syndrome. nine0006
What we did
We analyzed combinations of serum screening tests in the first (up to 14 weeks) and second (up to 24 weeks) trimesters of pregnancy with or without ultrasound screening in the first trimester. Our goal was to identify the most accurate tests for predicting the risk of Down syndrome during pregnancy. One ultrasound index (neckfold thickness) and seven different serological indexes (PAPP-A, total hCG, free beta-hCG, unbound estriol, alpha-fetoprotein, inhibin A, ADAM 12) were studied, which can be used separately, in ratios or in combination with each other, obtained before 24 weeks of gestation, thereby obtaining 32 screening tests for the detection of Down's syndrome.
We found 22 studies involving 228615 pregnant women (including 1067 fetuses with Down syndrome). nine0004
What we found
During Down Syndrome screening, which included tests during the first and second trimesters that combined to determine overall risk, we found that a test that included neckfold measurement and PAPP- A in the first trimester, as well as the determination of total hCG, unbound estriol, alpha-fetoprotein and inhibin A in the second trimester, turned out to be the most sensitive, as it allowed to determine 9out of 10 pregnancies associated with Down syndrome. Five percent of pregnant women who were determined to be at high risk on this combination of tests would not have a child with Down syndrome. There have been relatively few studies evaluating these tests, so we cannot draw firm conclusions or recommendations about which test is best.
Other important information to consider
Ultrasounds by themselves have no adverse effects on women, and blood tests can cause discomfort, bruising, and, in rare cases, infection.
However, some women who have a high-risk Down syndrome baby on screening and who have had an amniocentesis or CVS are at risk of miscarriage of a non-Down syndrome baby. Parents will need to weigh this risk when deciding whether to perform amniocentesis or CVS after a "high risk" screening test is identified. nine0006
Translation notes:
Translation: Abuzyarova Daria Leonidovna. Editing: Prosyukova Ksenia Olegovna, Yudina Ekaterina Viktorovna. Project coordination for translation into Russian: Cochrane Russia - Cochrane Russia (branch of the Northern Cochrane Center on the basis of Kazan Federal University). For questions related to this translation, please contact us at: [email protected]; [email protected]
Down Syndrome Screening - Bahçeci IVF Clinic
The desire of every parent-to-be is to have a healthy child. During pregnancy, various tests are used to assess the health of the unborn baby. Tests such as ultrasounds and blood tests are used during pregnancy for screening purposes.
What is Screening?
Tests called screening tests are used to detect a specific disease in healthy people. Thanks to these tests, it is possible to intervene during the course of the disease, either before it occurs or at an early stage. The main screening tests for women's health are breast ultrasound for breast cancer and the PAP smear test for cervical cancer. But screening is not a diagnostic test. Additional tests are needed to confirm the diagnosis in patients at high risk of developing the disease. For example, taking a tissue sample (biopsy) from a suspicious area. These tests are called "diagnostic" tests. nine0006
Why Are Diagnostic Tests Not Used Right Away?
Screening tests are tests that can be applied to all people, are inexpensive, and cause the least discomfort to patients. Diagnostic tests are expensive operations that require special interventions, knowledge and equipment. For example, to diagnose Down's syndrome, it is necessary to perform an amniocentesis (analysis of the amniotic fluid in which the baby is located).
This procedure requires an experienced doctor, ultrasound, as well as a genetic laboratory and a specialist geneticist for chromosome analysis. Because of the risks and costs associated with them, diagnostic tests are only performed on pregnant women who have been identified as “high risk” of the disease. nine0006
What is a Chromosome?
Chromosomal cells are the building blocks that contain the genetic information that makes us who we are and passes that information on to our children. Humans have 23 pairs of chromosomes. The pair of these chromosomes are the sex chromosomes (XY in males; XX in females).
What is Down Syndrome?
Down syndrome (trisomy 21) is a genetic disorder caused by an excess of part or all of chromosome 21. Children with Down syndrome have mild or severe mental retardation, learning difficulties, and physical retardation. They are also at high risk for heart abnormalities, reflux, recurrent ear infections, sleep disturbances, and thyroid disease.
One child with Down syndrome is born in 800-1000 children. nine0006
How is Down Syndrome screened during pregnancy?
At 10-14 and 16-18 weeks of pregnancy, biochemical tests of the mother's blood are performed. At weeks 10-14, free beta hCG and PAPP-A tests are done, and at weeks 16-18, alpha-fetoprotein, beta-hCG and estriol levels are checked. These tests are not "intelligence tests". As you know, IQ tests are written and oral exams, not blood tests. Therefore, the definition of "intellectual test" is used incorrectly. nine0006
First Trimester Screening
Obstetricians describe the pregnancy process by dividing it into three periods (trimesters). The first 14 weeks are called the first trimester. Between 10 and 14 weeks of pregnancy, your doctor will use ultrasound to measure your baby's age, heart rate, and nasal bone. Also at this time, the child's collar zone (NT) is measured.
Second Trimester Screening
In the second trimester of pregnancy, between 16 and 18 weeks, the next screening is done.
A blood sample is taken from the expectant mother and examined for alpha-fetoprotein, beta hCG and estriol. The risk is calculated from the results of these tests. nine0006
What are the Risks?
So what does high risk and low risk mean?
The screening test is not a diagnostic test. Its goal is to refer only pregnant women at high risk of having a baby with Down's syndrome for further, more serious investigations (chromosomal analysis and amniocentesis).
A “high risk” or “positive” test result does not mean your child has Down syndrome. On the other hand, "low risk" or "negative" does not mean that your child will not have Down syndrome either. According to statistics, out of 10 children with Down syndrome, screening reveals 9, but one baby with this diagnosis is born into the world.
Is screening done for multiple pregnancies?
In multiple pregnancies, maternal blood counts are not used for screening purposes. Between 10 and 14 weeks of pregnancy, measurements of the collar zone and nasal bone are taken, and ultrasound is done in the second trimester.
