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.
Risk factors
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:
1. Alpha-fetoprotein (AFP)
2. Free B-human chorionic gonadotrophin
3. Unconjugated estriol
4. Inhibin-A
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.
