The First Trimester Screening test is appropriate if you would like to evaluate the risk for chromosome abnormalities including Down’s Syndrome, Edward Syndrome and Patau Syndrome.
At the end of the first trimester, normally there is a small amount of fluid seen beneath the skin of fetal neck and head. This fluid space is called as nuchal translucency. In an ultrasound image this is identified as the echo free space at the back of the fetal neck and can be accurately measured to within a tenth of a millimeter. All fetuses have a measurable nuchal translucency. This scan is ideally performed between 12 weeks and 13 weeks 6 days of your pregnancy. When there is extra fluid, ie when the nuchal translucency measurement is thicker than normal, there is an association with chromosomal anomalies such as Down Syndrome and some structural abnormalities in the fetus.
This scan is ideally performed between 12 weeks and 13 weeks 6 days of your pregnancy. During this time, there is a small amount of fluid beneath the skin of your baby’s neck. This fluid space is called the nuchal translucency.
When there is extra fluid, ie when the nuchal translucency measurement is thicker than normal, there is an association with chromosomal anomalies such as Down Syndrome and some structural abnormalities in the fetus.
Our experienced Doctor and Sonographers are trained to the highest standards to perform these specialist measurements of you and your baby.
What is involved in first trimester screening test?
There are two separate components to first trimester screening.
- A blood test (ideally done at 10 weeks)
- Nuchal translucency scan (ideally done at 12-13 weeks)
The results of the blood test, scan findings and maternal details are fed into a computer package (developed by Fetal Medicine Foundation, London) which then calculates the individual risk for chromosome abnormalities. This will either be ‘low risk’ (risk is less than 1in 300) or a ‘high risk’ (risk is greater than 1in 300).
What information is obtained from blood test?
Beta human chorionic gonadotropin (Free- BhCG) and pregnancy associated plasma protein- A (PAPP-A) levels are assessed from the blood test. Though this test is best done at 10weeks, it can be done just before or on the same day as the scan. In fetuses affected by chromosomal abnormalities the levels of these hormones are frequently abnormal.
When will I get the results?
If you have already had your blood test and results are available at the time of your scan, we will be able to give you the results immediately after your scan. If you haven’t had the blood test, we will need to wait until the blood results become available to assess your risk.
What happens if my test result is ‘high risk’?
If you want to have a definitive result to 100% exclude a chromosome abnormality, you should then consider having prenatal diagnostic testing either with CVS or Amniocentesis. It is best to talk to your Doctor about your options.
How accurate is the test?
The combined First trimester Screening is the most sensitive and specific screening test for Down syndrome. It detects 90% of chromosomal abnormalities. This means that no matter how low the risk is calculated to be, a chromosomal abnormality like Down syndrome is not completely excluded.
What are the limitations of this test?
A low risk screening result does not guarantee your baby does not have a chromosomal disorder. It is only a screening test and does not actually tell you whether your baby does or does not have a chromosomal disorder. The test can miss about 10% of chromosomally abnormal fetuses.
In addition, a low risk result does not mean that your baby will be born healthy, though majority of babies are healthy at birth.
First trimester screening is offered to all women during their pregnancy. It is a voluntary test where you can ‘opt out’ if you think it is not an appropriate test for you. You should discuss with your partner and the doctor before deciding to proceed with the testing.