Down's syndrome tests at 12 weeks

Screening for Down's syndrome, Edwards' syndrome and Patau's syndrome

You will be offered a screening test for Down's syndrome, Edwards' syndrome and Patau's syndrome between 10 and 14 weeks of pregnancy. This is to assess your chances of having a baby with one of these conditions.

Down's syndrome is also called trisomy 21 or T21. Edwards' syndrome is also called trisomy 18 or T18, and Patau's syndrome is also called trisomy 13 or T13.

If a screening test shows that you have a higher chance of having a baby with Down's syndrome, Edwards' syndrome or Patau's syndrome, you'll be offered further tests to find out for certain if your baby has the condition.

What are Down's syndrome, Edwards' syndrome and Patau's syndrome?

Down's syndrome

Down's syndrome causes some level of learning disability.

People with Down's syndrome may be more likely to have other health conditions, such as heart conditions, and problems with the digestive system, hearing and vision. Sometimes these can be serious, but many can be treated.

Edwards' syndrome and Patau's syndrome

Sadly, most babies with Edwards' syndrome or Patau's syndrome will die before or shortly after birth. Some babies may survive to adulthood, but this is rare.

All babies born with Edwards' syndrome or Patau's syndrome will have a wide range of problems, which can be very serious. These may include major complications affecting their brain.

Read more about Edwards' syndrome and Patau's syndrome.

What does screening for Down's syndrome, Edwards' syndrome and Patau's syndrome involve?

Combined test

A screening test for Down's syndrome, Edwards' syndrome and Patau's syndrome is available between weeks 10 and 14 of pregnancy. It's called the combined test because it combines an ultrasound scan with a blood test. The blood test can be carried out at the same time as the 12-week scan.

If you choose to have the test, you will have a blood sample taken. At the scan, the fluid at the back of the baby's neck is measured to determine the "nuchal translucency". Your age and the information from these 2 tests are used to work out the chance of the baby having Down's syndrome, Edwards' syndrome or Patau's syndrome.

Obtaining a nuchal translucency measurement depends on the position of the baby and is not always possible. If this is the case, you will be offered a different blood screening test, called the quadruple test, when you're 14 to 20 weeks pregnant.

Quadruple blood screening test

If it was not possible to obtain a nuchal translucency measurement, or you're more than 14 weeks into your pregnancy, you'll be offered a test called the quadruple blood screening test between 14 and 20 weeks of pregnancy. This only screens for Down's syndrome and is not as accurate as the combined test.

20-week screening scan

For Edwards' syndrome and Patau's syndrome, if you are too far into your pregnancy to have the combined test, you'll be offered a 20-week screening scan. This looks for physical conditions, including Edwards' syndrome and Patau's syndrome.

Can this screening test harm me or my baby?

The screening test cannot harm you or the baby, but it's important to consider carefully whether to have this test.

It cannot tell you for certain whether the baby does or does not have Down's syndrome, Edward's syndrome or Patau's syndrome, but it can provide information that may lead to further important decisions. For example, you may be offered diagnostic tests that can tell you for certain whether the baby has these conditions, but these tests have a risk of miscarriage.

Do I need to have screening for Down's syndrome, Edwards' syndrome and Patau's syndrome?

You do not need to have this screening test – it's your choice. Some people want to find out the chance of their baby having these conditions while others do not.

You can choose to have screening for:

all 3 conditions
Down's syndrome only
Edwards' syndrome and Patau's syndrome only
none of the conditions

What if I decide not to have this test?

If you choose not to have the screening test for Down's syndrome, Edwards' syndrome or Patau's syndrome, you can still choose to have other tests, such as a 12-week scan.

If you choose not to have the screening test for these conditions, it's important to understand that if you have a scan at any point during your pregnancy, it could pick up physical conditions.

The person scanning you will always tell you if any conditions are found.

Getting your results

The screening test will not tell you whether your baby does or does not have Down's, Edwards' or Patau's syndromes – it will tell you if you have a higher or lower chance of having a baby with one of these conditions.

If you have screening for all 3 conditions, you will receive 2 results: 1 for your chance of having a baby with Down's syndrome, and 1 for your joint chance of having a baby with Edwards' syndrome or Patau's syndrome.

If your screening test returns a lower-chance result, you should be told within 2 weeks. If it shows a higher chance, you should be told within 3 working days of the result being available.

This may take a little longer if your test is sent to another hospital. It may be worth asking the midwife what happens in your area and when you can expect to get your results.

You will be offered an appointment to discuss the test results and the options you have.

The charity Antenatal Results and Choices (ARC) offers lots of information about screening results and your options if you get a higher-chance result.

Possible results

Lower-chance result

If the screening test shows that the chance of having a baby with Down's syndrome, Edwards' syndrome and Patau's syndrome is lower than 1 in 150, this is a lower-chance result. More than 95 out of 100 screening test results will be lower chance.

A lower-chance result does not mean there's no chance at all of the baby having Down's syndrome, Edwards' syndrome or Patau's syndrome.

Higher-chance result

If the screening test shows that the chance of the baby having Down's syndrome, Edwards' syndrome or Patau's syndrome is higher than 1 in 150 – that is, anywhere between 1 in 2 and 1 in 150 – this is called a higher-chance result.

Fewer than 1 in 20 results will be higher chance. This means that out of 100 pregnancies screened for Down's syndrome, Edwards' syndrome and Patau's syndrome, fewer than 5 will have a higher-chance result.

A higher-chance result does not mean the baby definitely has Down's syndrome, Edwards' syndrome or Patau's syndrome.

Will I need further tests?

If you have a lower-chance result, you will not be offered a further test.

If you have a higher-chance result, you can decide to:

not have any further testing
have a second screening test called non-invasive prenatal testing (NIPT) – this is a blood test, which can give you a more accurate screening result and help you to decide whether to have a diagnostic test or not
have a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS) straight away – this will tell you for certain whether or not your baby has Down's syndrome, Edwards' syndrome or Patau's syndrome, but in rare cases can cause a miscarriage

You can decide to have NIPT for:

all 3 conditions
Down's syndrome only
Edwards' syndrome and Patau's syndrome only

You can also decide to have a diagnostic test after NIPT.

NIPT is completely safe and will not harm your baby.

Discuss with your healthcare professional which tests are right for you.

Whatever results you get from any of the screening or diagnostic tests, you will get care and support to help you to decide what to do next.

If you find out your unborn baby has Down's syndrome, Edwards' syndrome or Patau's syndrome

If you find out your baby has Down's syndrome, Edwards' syndrome or Patau's syndrome a specialist doctor (obstetrician) or midwife will talk to you about your options .

You can read more about what happens if antenatal screening tests find something.

You may decide to continue with the pregnancy and prepare for your child with the condition.

Or you may decide that you do not want to continue with the pregnancy and have a termination.

If you are faced with this choice, you will get support from health professionals to help you make your decision.

For more information see GOV.UK: Screening tests for you and your baby

The charity Antenatal Results and Choices (ARC) runs a helpline from Monday to Friday, 10am to 5.30pm on 020 7713 7486.

The Down's Syndrome Association also has useful information on screening.

The charity SOFT UK offers information and support through diagnosis, bereavement, pregnancy decisions and caring for all UK families affected by Edwards' syndrome (T18) or Patau's syndrome (T13).

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.

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.

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.

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).

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.

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]

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