How Do They Test For Down Syndrome During Pregnancy

I Am Pregnant Will I Have Both First And Second Trimester Screening Performed

Testing for Down Syndrome (During My Pregnancy)

There are several approaches to screening depending on what technology is available where you are and when you first visit your healthcare practitioner for prenatal care. Options include:

First trimester screening for chromosome abnormalities using the combined tests for PAPP-A, hCG and nuchal translucency ultrasound , followed by a blood test for maternal AFP and/or a fetal ultrasound in the second trimester to check for neural tube defects

Second trimester maternal serum screening to assess risk for chromosome abnormalities and neural tube defects this may be the only testing done, especially in the case of women who do not visit their healthcare practitioner until the second trimester.

Cell-free fetal DNA testing in the first or second trimester, followed by a blood test for maternal AFP and/or a fetal ultrasound in the second trimester to check for neural tube defects

Typically, if first trimester screening for chromosome disorders has been performed, then screening in the second trimester is not performed because the risks for Down syndrome and Edwards syndrome have already been assessed. However, if you and your healthcare practitioner wish to use the results of both the first trimester Down syndrome screen combined tests and the second trimester maternal serum screen to assess the risk of chromosome abnormalities, then one of the following approaches is used:

The Two Types Of Prenatal Tests For Down Syndrome

Health care professionals can offer down syndrome checks during the early stages of pregnancy, or after the baby is born. Here are the two types of tests:

  • Screening Tests: Technically, screening tests do not provide a definitive answer, however, it can tell you if your baby is at a high risk of down syndrome. It is also a harmless method for the mother and baby.
  • Diagnostic Tests: The accuracy of this test determines that down syndrome is present. The downside of this test is the possibility of miscarriage. And because of the risk, they are only suggested to women with babies that have an increased risk of down syndrome, based on the result of the screening test.

Pregnant women do not have to undergo these tests if they do not want to. If the baby has an increased risk of the down syndrome from the initial screening test, it is not mandatory to continue with the diagnostic testing. If you think that the risk is not worth it, then you can discuss this with your doctor.

What Screening Tests Are Available

There are two basic methods of screening for Down’s syndrome – the ultrasound scan and biochemical serum screening:

Nuchal translucency ultrasound scan : this is a special ultrasound scan that is done between 11 weeks and 2 days and 14 weeks and 1 day of pregnancy. It may be done at the same time as your early dating scan and is carried out in the same way. It measures the fluid collection under the skin at the back of the baby’s neck ).

All babies have a collection of fluid here but babies with Down’s syndrome tend to have more fluid in this area. The fluid measurement, your age, the size of the baby and other details such as your weight, ethnicity and smoking status are then put into a computer program to give the risk of the baby having Down’s syndrome.

Sometimes it may be difficult to obtain an accurate measurement of the NT. This may be due to the position of the baby or because the pregnant woman is overweight.

Blood tests : blood tests may be done to measure levels of various hormones and proteins in your blood. These hormones and proteins are produced by the placenta or the developing baby.

Examples include pregnancy-associated plasma protein A , beta human chorionic gonadotrophin and alpha-fetoprotein . If the baby has Down’s syndrome, the levels of these substances can be affected.

The two main screening tests used for Down’s syndrome using the above methods are:

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Understanding What The Nipt Test Results Mean

The NIPT measures the fetal cfDNA in the mothers bloodstream, which comes from the placenta. This is called the fetal fraction. For the most accurate test results possible, the fetal fraction must be over 4 percent. This usually happens around the 10th week of pregnancy and this is why the test is recommended after this time.

There are several ways the fetal cfDNA can be analyzed. The most common way is to determine the amount of both maternal and fetal cfDNA. The test will look at specific chromosomes to see if the percentage of cfDNA from each of these chromosomes is considered normal.

If it falls within the standard range, the result will be negative. This means the fetus has a risk of the genetic conditions caused by the chromosomes in question.

If the cfDNA is more than the standard range, this could lead to a positive result, meaning the fetus may have an increased risk of a genetic condition. But please be reassured of this: NIPT is not 100 percent conclusive. Positive results require further testing to confirm any true-positive fetal chromosomal abnormality or related disorder.

We do also have to mention that there is also a very low risk of getting a false negative NIPT result. In this case, a baby could be born with a genetic abnormality that was not detected with the NIPT or additional screenings throughout the course of pregnancy.

Its important to reiterate, however, that the test is not 100 percent accurate or diagnostic.

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It comes down to your level of concern about the results. I’ve had plenty of patients who opt for Down syndrome screening and, when the results show elevated risk, decide not to pursue diagnostic testing. That decision is completely OK.

However, you might want to have more certainty whether your child has a genetic condition and potentially which one. Some patients choose to undergo genetic testing to get more information and feel more prepared, while others prefer not to know for their own personal reasons. It’s entirely the parents’ choice.

If you do want to know more, we can perform further testing. Talk to your provider, who can recommend the most appropriate test. Certain diagnostic tests are available only during certain trimesters and some carry a risk of pregnancy loss. Also, keep in mind that some tests require a longer waiting period to return results.

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Are There Any Risks To The Tests

There is very little risk to having a blood test or ultrasound. After a blood test, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Amniocentesis, CVS, and PUBS tests are usually very safe procedures, but they do have a slight risk of causing a miscarriage.

When Will I Be Offered Screening

Different screening tests are offered at different times during pregnancy.

The screening test for sickle cell and thalassaemia should be offered as early as possible before 10 weeks of pregnancy.

It’s recommended that screening blood tests for HIV, hepatitis B and syphilis should happen as early as possible in pregnancy.

This is so you can be offered specialist care and treatment to protect your health and reduce the chance of your baby getting infected.

These blood tests should not be delayed until the first scan appointment.

You’ll be offered screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome around the time of your dating scan, which happens when you’re around 11 to 14 weeks pregnant.

You’ll be offered screening to check your baby’s development at a 20-week scan when you’re around 18 to 21 weeks pregnant.

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How Do I Interpret The Results Of The Screening Test

As mentioned above, the screening test will give the risk in this pregnancy of the baby being born with Down’s syndrome. For example, the test may show that there is a 1 in 1,000 risk of having a baby with Down’s syndrome. This means that for every 1,000 pregnant women, one will have a baby born with Down’s syndrome and 999 will have a baby born without Down’s syndrome. So, this would be quite a low risk.

In the UK, the National Screening Committee has suggested a cut-off level to differentiate between screening test results with a higher risk that the baby is born with Down’s syndrome and those with a lower risk.

The cut off is 1 in 150. This means that if your screening test results show a risk of between 1 in 2 to 1 in 150 that the baby has Down’s syndrome, this is classified as a higher risk result. If the results show a risk of 1 in 151 or more, this is classified as a lower risk result. The higher the second number gets, the lower the risk becomes .

So, when you are given your results, you will be told whether this is a lower risk or a higher risk result.

Screening Tests For Down Syndrome

Down Syndrome test during pregnancy | Benefits of GENETIC TESTING in the first Trimester | NIPT TEST

A Down syndrome screening test is a test that does not carry any risk to your pregnancy. It collects information about your baby, and gives a guide as to how likely it is to have Down syndrome in the current pregnancy. This is expressed as a risk of Down syndrome. However, it is not 100%, so it does not tell you that a baby does or does not have the condition definitively. This is important, as Down syndrome can still occur with a low risk result, and conversely, people with a high risk result will not always have a baby with Down syndrome.

There are currently 2 good screening tests for Down syndrome, the combined first trimester screening test and the non-invasive prenatal test . These are available to all women.

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Combined First Trimester Screening

The combined first trimester screening test is done between 9 weeks and 13 weeks into the pregnancy to calculate the chance of a number of abnormalities, including Down syndrome. It is safe for both mother and baby. There will usually be a cost, but you can claim some of it back from Medicare.

A computer is used to combine results from 2 tests:

  • A blood test, done between 9 and 12 weeks into the pregnancy, looks for hormonal changes that can suggest there is a problem with the babys chromosomes.
  • An ultrasound scan, done at 12 to 13 weeks into the pregnancy, measures the thickness of fluid behind the babys neck, called the nuchal translucency. This is often larger in babies with Down syndrome.

These results, combined with the mothers age, show the chance of Down syndrome. If the baby is at increased chance, you will be offered a diagnostic test, which is optional, to confirm whether or not the baby has Down syndrome.

Prenatal Screening For Down Syndrome

There are several options for Down syndrome prenatal screening. These include:

  • A blood test and an ultrasound test during the first trimester of pregnancy. This is the most accepted approach for screening during the first trimester. A blood test enables a health care provider to check for “markers,” such as certain proteins, in the mother’s blood that suggest an increased likelihood of Down syndrome.2 Then the health care provider does an ultrasound test, which uses high-frequency sound waves to create images. An ultrasound can detect fluid at the back of a fetus’s neck, which sometimes indicates Down syndrome. The ultrasound test is called measurement of nuchal translucency. During the first trimester, this combined method results in more effective or comparable detection rates than methods used during the second trimester.3
  • A blood test during the second trimester of pregnancy. As in the first trimester, a blood test enables a health care provider to check for markers in the mother’s blood. A triple screen looks for levels of three different markers a quadruple screen looks for levels of four different markers.3,4
  • A combined test . This approach uses both a blood test and an ultrasound during the first trimester as well as a second-trimester blood test. Health care providers then combine all these results to produce one Down syndrome risk rating.2

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What Are The Reasons To Test Or Not Test

The reasons to test or not test vary from person to person and couple to couple.Performing the tests and confirming the diagnosis provides you with certain opportunities:

  • Begin planning for a child with special needs
  • Start addressing anticipated lifestyle changes
  • Identify support groups and resources

Some individuals or couples may elect not to pursue testing or additional testing for various reasons:

  • They are comfortable with the results no matter what the outcome is
  • Because of personal, moral, or religious reasons, the decision about carrying the child to term is not an option
  • Risk of harming the developing baby

It is important to discuss the risks and benefits of testing thoroughly with your health care provider. Your health care provider will help you decide if the benefits from the results could outweigh any risks from the procedure.

Is Testing For Down Syndrome Necessary


Research says that in Australia, 1 in 1,100 babies is born with Down Syndrome. Down Syndrome is a genetic disorder that affects a certain level of intellectual disability and physical developmental delay. There are 23 chromosomes in each cell of a human body, a baby diagnosed with down syndrome, is born with an extra chromosome 21 present in their cells. Down Syndrome is also known as Trisomy 21. This usually occurs at random during the time of conception. The adverse effects of down syndrome are usually delayed in physical growth, and intellectual disability However, the most recognizable trait is characteristic facial features. Intellectual disability varies widely. The average IQ of a teen or adult person with down syndrome is equal to the mental capacity of an 8- or 9-year-old child.

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Video: Screening For You And Your Baby

This video shows which tests are available during pregnancy and after your baby has been born.

You can watch translated versions of this video on Vimeo.

You’ll be offered some screening tests during pregnancy to try to find any health conditions that could affect you or your baby.

The tests can help you make choices about further tests and care or treatment during your pregnancy or after your baby’s born. All screening tests offered by the NHS are free.

How Are The Tests Done

For the nuchal translucency test, your doctor or an ultrasound technologist spreads a gel on your belly. Then he or she gently moves a hand-held device called a transducer over your belly. Images of the baby are displayed on a monitor. The doctor can look for and measure the thickness at the back of the baby’s neck.

A simple blood test is all that’s needed for the rest of the first-trimester screening.

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

There are no known physical risks to having the tests, other than a possible bruise on your arm from the blood test.

The doctor looks at the test resultsalong with your age and other factorsto find out the chance that your baby may have certain problems.

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What Is Being Tested

The first trimester screening is a combination of two blood tests and a special ultrasound that are used to assess a pregnant womans risk of carrying a baby with Down syndrome or Edwards syndrome . Performing and evaluating them together, plus considering the womans age, increases both the sensitivity and specificity of the screening results.

  • Pregnancy-associated plasma protein A is a

The first trimester screening is a combination of two blood tests and a special ultrasound that are used to assess a pregnant womans risk of carrying a baby with Down syndrome or Edwards syndrome . Performing and evaluating them together, plus considering the womans age, increases both the sensitivity and specificity of the screening results.

If the results of first trimester screening are cause for concern, diagnostic tests such as amniocentesis or chorionic villus sampling may be recommended.

Taking Account Of Screening In A Previous Pregnancy

What tests during pregnancy can confirm Down Syndrome?

If a woman has been screened for Downs syndrome or open neural tube defects in a previous pregnancy the levels of the screening markers in that pregnancy can be used to adjust the marker levels in the current pregnancy. This is useful because markers used in screening tend to ‘track’ between pregnancy . So a woman with a false positive result in one pregnancy is likely to have a false positive result again in a subsequent pregnancy. Adjusting marker levels for those in a previous pregnancy can help avoid this problem of false-positives recurring in different pregnancies.

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What Are My Options If The Results Of The Diagnostic Test Are Abnormal

Before you leave the hospital, someone will ask you how you would like to receive the results of your CVS or amniocentesis. You can usually choose whether to receive the results by phone or come into the hospital again and receive your results face-to-face. In some cases, a community midwife may be able to come to your home to give you the results. You will also receive written confirmation of your results.

For most women, the laboratory test will give a definite ‘yes’ or ‘no’ answer. These results will let you know whether your baby has the chromosomal abnormality the test was looking for.

Most women who have CVS or amniocentesis will have a ‘normal’ result .

Some women will be told their baby has the chromosomal abnormality the test was looking for. If your baby is diagnosed with a chromosomal abnormality, your doctor or midwife will give you information on the condition your baby has and they will give you the opportunity to discuss this with a specialist.

Very occasionally, women who have CVS or amniocentesis to detect Down’s syndrome find out their baby has a different chromosomal abnormality. If this happens to you, your doctor or midwife will give you information on the condition your baby has and they will give you the opportunity to discuss this with a specialist.

These decisions are often very difficult and you might want to talk about your feelings with a midwife, doctor or a support organisation for parents, such as Antenatal Results and Choices .

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