Chromosome testing for down syndrome

Prenatal Testing for Down Syndrome | Patient Education

Screening tests

All pregnant individuals in California have access to California prenatal screening (CA PNS), also called sequential integrated screening. This noninvasive process is carried out in two steps.

In the first step, which is performed when the pregnancy is between 10 and 14 weeks, a blood sample is taken from the pregnant person and a nuchal translucency ultrasound is performed to measure the fluid at the back of the baby's neck. If the blood test is scheduled prior to the ultrasound, we can provide those results at the end of your ultrasound appointment. The blood test results, nuchal translucency measurement and pregnant person's age are together used to estimate the risk for Down syndrome and trisomy 18 (a genetic condition, also called Edwards syndrome, that affects fetal development).

The second step is a test performed with a blood sample from the pregnant person when the pregnancy is between 15 and 20 weeks. 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 (a genetic condition that can slow growth and cause intellectual disability), an open neural tube defect (a problem with the formation of the embryo's nervous system, such as spina bifida) or an abdominal wall defect (an abnormal opening in the abdomen).

Diagnostic tests

Amniocentesis, chorionic villus sampling (CVS) and ultrasound are the three primary procedures for diagnostic testing.

Amniocentesis is the test we most commonly use to identify chromosomal problems, such as Down syndrome. (In at-risk fetuses, it can be used to detect other genetic diseases, such as cystic fibrosis, Tay-Sachs disease and sickle cell disease.)

An amniocentesis procedure for genetic testing is typically performed when the pregnancy is between 15 and 20 weeks. Under ultrasound guidance, a needle is inserted through the abdomen to remove a small sample of amniotic fluid. Cells from the fluid are cultured and a karyotype test – an analysis of the cells' chromosomal makeup – is performed. It takes about two weeks to receive the results. Amniocentesis detects most chromosomal disorders with a high degree of accuracy.

There is a low risk of miscarriage as a result of amniocentesis – about 1 in 900. Miscarriage rates for amniocentesis performed at UCSF are extremely low.

Like amniocentesis, chorionic villus sampling is most commonly used to identify chromosomal problems, such as Down syndrome. (It can also be used to detect other genetic diseases – including cystic fibrosis, Tay-Sachs disease and sickle cell disease – in at-risk fetuses.) The main advantage over amniocentesis is that CVS is done much earlier in pregnancy, at 10 to 13 weeks rather than 15 to 20 weeks.

CVS involves removing a tiny piece of tissue from the placenta for analysis. Under ultrasound guidance, this sample is obtained either with a needle inserted through the abdomen or a catheter inserted through the vagina and into the cervix (outer end of the uterus). The tissue is cultured and a karyotype test of the cells' chromosomal makeup is performed. It takes about two weeks to receive the results.

While it can provide information earlier in pregnancy than amniocentesis, CVS does not detect spinal cord defects. However, we can screen for spinal cord defects later in the pregnancy using expanded alpha-fetoprotein (AFP) blood testing or ultrasound.

There is a low risk of miscarriage as a result of CVS – about 1 in 450. Miscarriage rates for CVS procedures performed at UCSF are very low.

While the primary purpose of ultrasound is to determine the pregnancy's status – due date, size of the fetus and whether there's more than one baby – ultrasound can also provide some information about possible birth defects. All pregnant UCSF patients undergo a comprehensive ultrasound exam before any invasive tests are performed. We will explain your ultrasound results at the time of your visit.

In some patients, an ultrasound raises concern for a fetal abnormality. This possibility makes ultrasound expertise crucial, so you may find it reassuring that we have extensive experience in performing and interpreting ultrasound exams in pregnancy.

The meaning of a positive result

If you receive positive results on a screening test, we recommend that you discuss its implications and your options with your doctor and a genetic counselor. They will explain what types of diagnostic testing are available. Whether to have invasive genetic testing is your decision.

If a diagnostic test finds a genetic abnormality, we recommend discussing the significance of the result with experts on the condition, including a medical geneticist and a genetic counselor, as well as your doctor.

Down syndrome - Diagnosis and treatment

Diagnosis

The American College of Obstetricians and Gynecologists recommends offering the option of screening tests and diagnostic tests for Down syndrome to all pregnant women, regardless of age.

Screening tests can indicate the likelihood or chances that a mother is carrying a baby with Down syndrome. But these tests can't tell for sure or diagnose whether the baby has Down syndrome.
Diagnostic tests can identify or diagnose whether your baby has Down syndrome.

Your health care provider can discuss the types of tests, advantages and disadvantages, benefits and risks, and the meaning of your results. If appropriate, your provider may recommend that you talk to a genetics counselor.

Screening tests during pregnancy

Screening for Down syndrome is offered as a routine part of prenatal care. Although screening tests can only identify your risk of carrying a baby with Down syndrome, they can help you make decisions about more-specific diagnostic tests.

Screening tests include the first trimester combined test and the integrated screening test.

The first trimester combined test

The first trimester combined test, which is done in two steps, includes:

Blood test. This blood test measures the levels of pregnancy-associated plasma protein-A (PAPP-A) and the pregnancy hormone known as human chorionic gonadotropin (HCG). Abnormal levels of PAPP-A and HCG may indicate a problem with the baby.
Nuchal translucency test. During this test, an ultrasound is used to measure a specific area on the back of your baby's neck. This is known as a nuchal translucency screening test. When abnormalities are present, more fluid than usual tends to collect in this neck tissue.

Using your age and the results of the blood test and the ultrasound, your doctor or genetic counselor can estimate your risk of having a baby with Down syndrome.

Integrated screening test

The integrated screening test is done in two parts during the first and second trimesters of pregnancy. The results are combined to estimate the risk that your baby has Down syndrome.

First trimester. Part one includes a blood test to measure PAPP-A and an ultrasound to measure nuchal translucency.
Second trimester. The quad screen measures your blood level of four pregnancy-associated substances: alpha fetoprotein, estriol, HCG and inhibin A.

Diagnostic tests during pregnancy

If your screening test results are positive or worrisome, or you're at high risk of having a baby with Down syndrome, you might consider more testing to confirm the diagnosis. Your health care provider can help you weigh the pros and cons of these tests.

Diagnostic tests that can identify Down syndrome include:

Chorionic villus sampling (CVS). In CVS, cells are taken from the placenta and used to analyze the fetal chromosomes. This test is typically performed in the first trimester, between 10 and 13 weeks of pregnancy. The risk of pregnancy loss (miscarriage) from a CVS is very low.
Amniocentesis. A sample of the amniotic fluid surrounding the fetus is withdrawn through a needle inserted into the mother's uterus. This sample is then used to analyze the chromosomes of the fetus. Doctors usually perform this test in the second trimester, after 15 weeks of pregnancy. This test also carries a very low risk of miscarriage.

Preimplantation genetic diagnosis is an option for couples undergoing in vitro fertilization who are at increased risk of passing along certain genetic conditions. The embryo is tested for genetic abnormalities before it's implanted in the womb.

Diagnostic tests for newborns

After birth, the initial diagnosis of Down syndrome is often based on the baby's appearance. But the features associated with Down syndrome can be found in babies without Down syndrome, so your health care provider will likely order a test called a chromosomal karyotype to confirm diagnosis. Using a sample of blood, this test analyzes your child's chromosomes. If there's an extra chromosome 21 in all or some cells, the diagnosis is Down syndrome.

More Information

Amniocentesis
Genetic testing
Ultrasound

Treatment

Early intervention for infants and children with Down syndrome can make a major difference in improving their quality of life. Because each child with Down syndrome is unique, treatment will depend on individual needs. Also, different stages of life may require different services.

Team care

If your child has Down syndrome, you'll likely rely on a team of specialists that can provide medical care and help him or her develop skills as fully as possible. Depending on your child's particular needs, your team may include some of these experts:

Primary care pediatrician to coordinate and provide routine childhood care
Pediatric cardiologist
Pediatric gastroenterologist
Pediatric endocrinologist
Developmental pediatrician
Pediatric neurologist
Pediatric ear, nose and throat (ENT) specialist
Pediatric eye doctor (ophthalmologist)
Audiologist
Speech pathologist
Physical therapist
Occupational therapist

You'll need to make important decisions about your child's treatment and education. Build a team of health care providers, teachers and therapists you trust. These professionals can help evaluate the resources in your area and explain state and federal programs for children and adults with disabilities.

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Coping and support

When you learn your child has Down syndrome, you may experience a range of emotions, including anger, fear, worry and sorrow. You may not know what to expect, and you may worry about your ability to care for a child with a disability. The best antidote for fear and worry is information and support.

Consider these steps to prepare yourself and to care for your child:

Ask your health care provider about early intervention programs in your area. Available in most states, these special programs offer infants and young children with Down syndrome stimulation at an early age (typically until age 3) to help develop motor, language, social and self-help skills.
Learn about educational options for school. Depending on your child's needs, that may mean attending regular classes (mainstreaming), special education classes or both. With your health care team's recommendations, work with the school to understand and choose appropriate options.
Seek out other families who are dealing with the same issues. Most communities have support groups for parents of children with Down syndrome. You can also find internet support groups. Family and friends can also be a source of understanding and support.
Participate in social and leisure activities. Take time for family outings and look in your community for social activities such as park district programs, sports teams or ballet classes. Although some adaptations may be required, children and adults with Down syndrome can enjoy social and leisure activities.
Encourage independence. Your child's abilities may be different from other children's abilities, but with your support and some practice your child may be able to perform tasks such as packing lunch, managing hygiene and dressing, and doing light cooking and laundry.
Prepare for the transition to adulthood. Opportunities for living, working, and social and leisure activities can be explored before your child leaves school. Community living or group homes, and community employment, day programs or workshops after high school require some advance planning. Ask about opportunities and support in your area.

Expect a bright future. Most people with Down syndrome live with their families or independently, go to mainstream schools, read and write, participate in the community, and have jobs. People with Down syndrome can live fulfilling lives.

By Mayo Clinic Staff

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Down syndrome will be detected in the womb

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2799 24 April

The manufacturer of kits for genetic analysis "Sequenom Inc" has begun to release a prenatal test for the diagnosis of Down syndrome.

The MaterniT21 test is based on the sequencing of DNA circulating in maternal plasma. It detects DNA fragments belonging to chromosome 21. As a rule, chromosome 21 in the blood of a pregnant woman accounts for 1.35% of the total amount of maternal and fetal DNA. An excess amount of material on chromosome 21 indicates a genetic anomaly, namely trisomy on chromosome 21, which is a characteristic feature of Down syndrome.

Trisomy 21 means the presence of many pathological psychological and physical characteristics. In most cases, people with Down syndrome have intellectual disabilities, although in many cases they are not so significant. As a rule, this is slow speech, impaired motor skills. And outwardly they look a little different: they are characterized by rounded flat faces.

Down syndrome is often accompanied by congenital heart disease, hearing or vision problems, and thyroid dysfunction. The average life expectancy for people with Down syndrome is 55 years.

The difference between MaterniT21 and other previously available tests is that it is much more accurate and can also be used as early as the tenth week of pregnancy. And this will enable future parents to make the only right decision for them: whether to leave a child with Down syndrome, realizing all the possible consequences, or to terminate an unwanted pregnancy.

The company claims that the test has an accuracy of 9 in clinical studies published in Genetics in Medicine.9.1%. The test study evaluated blood samples from 212 women with pregnancies with a baby with Down syndrome and 1,484 blood samples from women pregnant with a baby without Down syndrome. The test identified 209 out of 212 Down syndrome children (98.6% accuracy), with a total of three false positives (0.2%) and three false negatives.

According to thestar.com

IMPORTANT!

The information in this section should not be used for self-diagnosis or self-treatment. In case of pain or other exacerbation of the disease, only the attending physician should prescribe diagnostic tests. For diagnosis and proper treatment, you should contact your doctor.
For a correct assessment of the results of your analyzes in dynamics, it is preferable to do studies in the same laboratory, since different laboratories may use different research methods and units of measurement to perform the same analyzes.

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Screening for Down's Syndrome - Bahçeci IVF Clinic

The desire of every future parent 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.

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.

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 to 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.

How is Down Syndrome screened during pregnancy?

At 10-14 and 16-18 weeks of pregnancy, biochemical analyzes 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.

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.

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” 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. However, it should be remembered that ultrasound evaluation is less accurate than maternal blood tests. Measurement of the collar zone in the first trimester allows you to correctly diagnose 7 out of 10 cases with Down syndrome.