14/06/2021
FIRST TRIMESTER ANOMALY SCAN ( 11- 14 WEEKS ) OR NT SCAN ESP FOR DOWN’S SYNDROME
The NT scan or Nuchal Translucency scan is a specialized scan to assess the risk for fetal chromosomal abnormalities in addition to the growth and development of the fetus.This is done between 11-14 weeks of pregnancy.We offer this scan as part of the first trimester screening for Down’s syndrome and as an early anomaly assessment to all our patients routinely.
When a baby is conceived, it inherits genetic material from its parents.The genetic material is usually transferred to the baby in the from of 46 chromosomes-23 from each parent.Therefore there are 46 chromosomes (arranged in 23 pairs) in each normal human cell.Most babies develops normally, but unfortunately a small number have significant problems.These problems may be due to structural defects or abnormalities in chromosomes and genes. Many structural defects can be detected by scanning but chromosomes and genes can not be checked by scanning alone. The scan forms a “screening method” to detect certain “markers” that place a fetus at “low risk or “ high risk” for down’s syndrome.
What is down’s syndrome?:
There are a number of chromosomal abnormalities , but Down’s syndrome or trisomy 21 is the most common. There is an extra chromosome of number 21 and hence the name trisomy 21. It causes severe learning disability in children. There is no cure for down’s syndrome.
How common is down’s syndrome ?
People do not usually except to have a baby with down’s syndrome. It does not usually run in families. Some people think that only older women can have a baby with down’s syndrome , but this is not true. Anyone can have a baby with down’s syndrome, but the risk does go up with age. The older a mother is the more chance she has of having a baby with the condition . For example , the chance of having a baby with down’s syndrome Is one in 1500 for women who are 20 years old, one in 900 for women who are 30 years old and one in 100 for who are 40 years. However, all pregnant women are at risk of carrying a baby affected by down’s syndrome .
What can you do to find out whether or not your baby has down’s syndrome?
There are two different types of test that can be done during pregnancy to look for down’s syndrome-screening tests and diagnostic tests. A screening test is offered to all women during early pregnancy to look at the chance in this pregnancy of the baby being born with down’s syndrome. It is important to understand that the screening test does not give a definite ‘yes’ or ‘no’ answer as to whether or not the baby does have down’s syndrome, you will usually be offered a diagnostic test.
What is first trimester combined screening?
This is a screening test done in the first trimester (before 14 weeks of pregnancy ) It is a combination of fetal ultrasound and maternal blood tests and Is called combined screening test .
Ultrasound : This ultrasound scan is called Nuchal Translucency scan (NT SCAN) Nuchal Translucency is the name for the fluid behind the neck of a fetus. An NT scan uses ultrasound to measure the amount to fluid.. A fetus at risk of down’s syndrome tends to have a higher amount of fluid. The thickness of the fluid can predict that the nuchal scan is performed between the 11th and 14th week of pregnancy , because the accuracy is best in the period.
Maternal blood test : On the day the scan is done a blood sample is taken from you. This blood test measures two substances (PAPP-A and B-HCG) , which are present in blood of all pregnant woman but abnormal levels are associated with enhanced risk of chromosomal problems in the fetus. We advise women to take the blood test between 10-11 weeks of pregnancy so that by the time they come for the next scan , the blood test results are available and the combined test report can be generated immediately following the scan.
Calculating risk : These two test reports are entered into a computer program along with your age to calculate a overall “risk “ or ratio of your baby having down’s syndrome. The calculated risk assessment is used to guide the discussion between you and your doctor about any further investigation or treatment. When used in combination which is down’s syndrome, but it also used for other abnormalities like trisomy 18, 13 , etc.
When will the report be available? The results of combined screening test will be available after the NT Scan in case in case the blood samples for the first trimester double marker have been given earlier. For women who choose to have the blood test on the day of the scan, the final combined test report will be ready within a week
Are there any risks with this test?
This test presents no risk to your baby . The main benefit is that because it is done in early pregnancy you can use the information to make an informed choice.
What happens if the test indicates a high risk (high chance) of chromosomal problem?
It is important to remember that this FTS will not diagnose down’s syndrome or other abnormalities. It only gives a risk assessment. You have to understand that if the risk is high, the only way to confirm the diagnosis is by testing for fetal chromosomes. These tests are chorionic villus sampling (CVS ) and amniocentesis.
What are the other advantages of doing this test?
1) Diagnose twins 2) To diagnose another detectable congenital anomalies 3) Pre eclampsia screening by testing the blood flow to the uterus (uterine artery Doppler) , which predicts IUGR and PRE ECLAMPSIA
What if you miss the tests: I e come after 14 weeks pregnancy ?
If you more than 14 weeks pregnant , combined screening can not be offered . Instead you will be offered quadruple test between 15-19 weeks pregnancy . After 20 weeks there are no screening tests
