This is basically an ultrasound combined with blood work; it is a non-invasive procedure. It is performed in two stages. During the first stage, a measurement of the fluid collected within the skin at the back of the fetus neck or nuchal fold, is made. This is usually conducted at 12 weeks (anytime between weeks 11-14 is ok); FYI all babies have nuchal folds.
The larger the measurement, the greater the odds for Down's syndrome. This scan is concurrently done with a blood test to enhance its effectiveness. With this combination, a detection rate of 85-89% can be achieved.
The main risk is that nuchal test alone does not produce accurate results. Other factors such as a blood test, your age and the stage of pregnancy have to be roped in.
The Procedure itself..
Nuchal translucency test & Blood test - stage 1
- Cold gel is applied on your abdomen
- A scanner moves over your skin with some pressure at certain points
- The captured images on the screen are explained by the technician to you
- The nuchal translucency is measured along with other indicators such as structural heart problems, shortened femur length (a bone in the leg), webbing between fingers
- There is also a possibility of looking at the fetus face to check for the presence of the nasal bone
- Baby's length will be assessed to confirm the due date
- The more indicators found, the higher the chance of following up with an amniocentesis
- A sample of your blood is taken at this stage to measure the concentration of 1 marker - pregnancy associated plasma protein-A.
- You will be given an appointment date for the second stage of the test
Blood test - stage 2
The second blood sample is taken at 14 weeks and not later than 20 weeks. This sample is to measure the concentration of 4 markers:
- Alpha-fetoprotein (AFP)
- Free B-human chorionic gonadotrophin
- Unconjugated estriol
A single screening result is derived by integrating both the stages. The nuchal scan measurement, your age and the levels of 5 markers (obtained from both the stages) are used to estimate your risk of Down's syndrome. The detection rate is 85%. The level of AFP in the second blood sample is used to predict if there is an increased risk of spina bifida or anencephaly. FYI, if AFP is abnormally low, it may suggest the baby could have Down's syndrome. It is important that both the ultrasound and blood sampling be done together to produce greater accuracy.
Down's Syndrome in brief
- When a sperm and egg unite, each brings 23 chromosomes; in Down's syndrome an extra chromosome is contributed
- This extra chromosome is called Trisomy 21 and can be detected through amniocentesis
- A Down's baby will be born with distinct features including slanting, closely set eyes, a short tongue, short neck and abnormal hands and feet
- They will be short all life and mentally retarded
- Some will also have congenital heart disease or respiratory problems
- In recent years, Down's children have been making great strides intellectually.