NT Scan
Thank you for choosing Mediplus Scans & Labs for Down Syndrome Screening Service…
Majority of pregnancies end happily with the birth of a healthy child. At the same time every pregnant woman has an inherent risk of delivering a baby with Downs syndrome. Prenatal screening is designed to identify women who are at a higher risk of delivering a baby with Down syndrome. Scientific research over the last two decades has shown that ultrasound between 11 to 13 weeks combined with a blood test for the pregnant women can help detect about 85%-90% of Down syndrome early.
What is Down’s syndrome?
Down’s Syndrome is a chromosomal abnormality where the child is born with an extra chromosome 21. This manifests as varying levels of mental disability, heart defects, low muscle tone and some gastrointestinal (stomach and bowel) defects. Down syndrome occurs in about I in 600 pregnancies all over the world. An ultrasound alone may not be able to pick up Downs syndrome and therefore there are screening tests for this. So the need for Downs screening is clearly important to the mother. While the mothers age of over 35, it increases the risk of Down syndrome. But almost 70% of Downs syndrome babies could be born to women below 35 years. Therefore, screening is offered to all women.
What does First trimester screening involve?
The screening involves an ultrasound scan and a blood test for the mother. Basic details about pregnancy such as the last menstrual period, previous pregnancies, medical history, date of birth and current weight will be collected. This information is needed for the risk prediction process.
The Nuchal Translucency (NT) Scan
- The first step of screening is Ultrasound which looks at the baby in detail. The length of the baby is measured to confirm the gestational age.
- The measurement is taken to assess the thickness of the fluid behind the neck of the baby (Nuchal Translucenty - NT)
- It is also seen if the baby is normal or if there are any abnormalities that can be visible or picked up at that time.
- The NT measurement has to be taken when the baby comes in a specific position. This may mean that the scan would take a longer time or even that there could be a wait for the baby to come to the correct position. This does not mean there is anything abnormal or wrong with the baby.
The Blood Test
Once the scan is satisfactory completed, a few ml of blood is taken to assess the special biochemical markers in the blood B-hCG and PAPP-A.
The Combined test (FTS)
The values of the scan measurements, the blood tests and the mother’s weight and age go through a software that predicts the risk of having a baby with Down syndrome.
The estimate of risk will be mentioned as a ratio eg 1:200 or 1:70. The ratio of 1:200 means that only one in 200 women will have Down syndrome baby.
The test only predicts a risk, it does not tell us if the baby is affected or not. The result of the test will say whether the woman is at “low risk” or “high risk” for Down syndrome. The risk cut off above which the mother will be called as high risk is 1:250.
When will the report be ready?
Scan report – same day. First trimester combined screening report will usually be given after 7 working days.
"Screen negative report" - What does it mean?
Screening negative means that the final risk number is greater than 250 cut off. eg 1:2000/1:5000. This places you in a low risk group and usually no further testing is advised.
“Screen Positive Report” – What does it mean?
If the risk predicted final number is lesser than cut off 250, it is termed as screen positive indicating an increased risk for Down syndrome. eg 1:50/1:20. It does not mean that the baby is affected. A further definitive test such as Chorionic villus sampling or Amniocentesis is indicated to confirm whether the baby is affected or not.
These tests are done under ultrasound guidance. Chorionic villi sampling (11-14 weeks) – a small amount of placental tissue is aspirated with the help of a needle.
Amniocentesis (After 16 weeks) – 20 ml of amniotic fluid is drawn and sent to the lab for genetic analysis. The report from the lab will indicate whether the baby has down syndrome or any other major structural chromosomal abnormality.
Amniocentesis (After 16 weeks) – 20 ml of amniotic fluid is drawn and sent to the lab for genetic analysis. The report from the lab will indicate whether the baby has down syndrome or any other major structural chromosomal abnormality.
