Patient Information

The 11-13+6 Weeks Scan/NT SCAN/FIRST TRIMESTER DOWN SYNDROME SCREENING


Ultrasound between 11-14 weeks of pregnancy is offered to all pregnant women to


• Confirm the number of fetus

• Date the pregnancy accurately

• Rule out major abnormalities like anencephaly, Holo prosencephaly. limb defects, major cardiac malformation etc.

• Screen for Down Syndrome


What is Down Syndrome ?

Down Syndrome (Trisomy 21) is the most common chromosomal cause of intellectual disability and is often associated with physical problems such as heart defects or difficulties in hearing. Incidence of down syndrome in India is approximately 1 in 800 live births.

All of us have 23 pairs of chromosomes. Down's syndrome is caused by the presence of an extra chromosomes (number 21) in the cells of the developing baby. Usually it is not inherited and so any baby can be affected even if there is no family history of Down's syndrome in the family.

We donot know exactly why babies get Down's syndrome. Although older women are more likely to have a baby with the condition, women of any age can have a baby with Down's syndrome. It is not caused by anything parents have done or not done..

The extra chromosome cannot be removed from cells, so there is no cure for the condition.

Age ( is years )
Risk of down syndrome
20
30
35
40
44
1 in 1500
1 in 900
1 in 350
1 in 100
1 in 30

• Should I have the tests for Down's syndrome?

Only the parents can decide that. some women, want to find out if their baby has Down syndrome, and some donot. Information about the tests and how they work can help you make up your mind.

• Will the tests tell me for certain if my baby has Down syndrome?

We begin by offering all women a screening test. Screening test help to predict if your baby has an increased risk of having Down syndrome.

We then offer diagnostic tests (Amino Centesis or Chorinic Villus sampling) that give definite information to the women at increased risk. Having a diagnostic test carries a small risk of miscarriage. That is why we offer a diagnostic test only to women with an increased risk.

• When is the test performed?

The combined test is performed between 11 weeks and 13 weeks + 6 days. (Length of the baby between 45-84 mm).

• What is a screening test and how is it done?

This test combines information from a scan of the baby and blood test from the mother. The scan measures a small collection of fluid at the back of a baby's neck (called nuchal translycency NT ). All babies have this fluid, but the amount is increased in babies with Down syndrome. The blood test measures two substances in mother's blood. These hormones are called PAPP-A (pregnancy associated plasma protein-A) and free B-HCG (B-human chorionic gonadotrophin.)

The results of nuchal translucency along with the blood test are combined with your age, weight and stage of pregnancy to estimate the risk of your baby having Down syndrome. A risk can also be calculated for multiple pregnancies. All our first trimester Down's risk assessment are done according to the fetal medicine foundation (FMF) protocol.


please note:

Having a thickened nuchal translucency (NT) can be associated with other fetal anomalies such as heart defects which will also be discussed in detail.


• can I do only the NT Scan?

Combining the results of the scan and blood gives a higher detection rate than the scan or blood test alone. The combined test detects about 90% pregnancies, (ie) 9 out of 10 women who have pregnancies with Down syndrome. The scan alone may detect only about 70%.


• What is Low risk or Screen Negative results?

If the screening test shows the risk of your baby having Down's syndrome is lower than the cut off 1 in 250, we will not offer you further tests. It doesnot mean that there is no risks at all that your baby has Down syndrome, just that it is unlikely.

• What happens is I have High risk or Screen positive result?

Overall about 3% women screened have a higher risk result and are offered a diagnostic test.

• Yon can decide not to have a diagnostic test


This caries no risk to your pregnancy but leaves some uncertainty until after your baby is born.


• You can decide to have a diagnostic test


A diagnostic test finds out for definite whether your baby has Down's syndrome or not. However a diagnostic test carries a small risk of miscarriage.


• Diagnostic tests for down's syndrome

There are two diagnostic test for Down syndrome

I. Chorionic villus sampling (CVS) and
2. Amniocentesis

A CVS is offered in early Pregnancy from II Weeks and involves taking a small sample of placental tissue (using local Anaesthetic) by inserting a needle through your abdominal wall.

It is Performed under ultrasound guidance. The results are normally available from 2-3 weeks. About 1: 300 of women who have a CVS will have a miscarriage.

An Amniocentesis can be performed from about 16 weeks of pregnancy and involves taking a sample of amniotic fluid from around the baby by inserting a needle through your abdominal wall. It is performed under ultrasound guidance to ensure that the needle is at a safe distance from your baby. The results can take up to 3 weeks. As with a CVS there is a risk of miscarriage of about 1:300. Whichever invasive test you may choose (depending on the stage of your pregnancy), if the results from the invasive test are negative it will rule out Down syndrome.


• What happens if my baby has down syndrome?

There are then two options. It is entirely the parents decision which one they choose. Some parents will decide to continue with the pregnancy, make plans and prepare for any extra challenges they might face bringing up a child with Down syndrome. Others may decide they don't want to continue with the pregnancy

You will have the opportunity to discuss your results

• Does the combined test check for other problems?

The measurements used as part of the combined test can also identity pregnancies at high risk of Edwards syndrome (Tiresomy 18) or Patau syndrome (Trisomy 13). Edwards and patau syndrome are rare but serious conditions and affected babies can have a range of several medical problems.

• During the scan we will check the main structures of your baby. As the baby is still very small, some problems can not be detected. That is why we always recommend that you have a further scan in mid pregnancy (The Detailed Scan) when the baby will be bigger.

Are there any alternatives to the combined test?

It your pregnancy is too advanced (more than 14 weeks plus one day) for the combined test to be done, we will offer you another blood test .This is called the quadruple test or QUAD test. This test can be done between 15 weeks to 20 weeks. The Quadruple test picks up around 80% of babies with downs syndrome . This is a blood test that measures 4 hormones in the mother's blood