Down’s Syndrome blood screening test
Down
syndrome is the most common birth abnormality in the US – each year around
6,000 babies are born with the condition.
Babies with Down syndrome have an extra chromosome 21 in
every cell, making three instead of the usual pair. This results in learning
difficulties and often heart or lung troubles. The physical appearance of a
person with Down syndrome is typical: distinctive wide-set eyes, short necks
and round faces.
The screening test for Down syndrome
Your
first trimester screen, which takes place around weeks 11-13 incorporates a nuchal translucency scan with a blood test to screen for
Down syndrome. Your blood will be screened for the pregnancy hormones human
chorionic gonadotropin (HCG) and pregnancy associated plasma protein PAPP-A,
low levels of which may indicate Down syndrome.
There
are also two second trimester blood tests that screen for the condition:
Quad screen This is carried out between 15 and 20
weeks and checks for the presence of four markers in your blood (alpha-fetoprotein, HCG, estriol and inhibin-A);
Triple screen
This is carried out between 16 and 18 weeks and checks for three markers
(alpha-fetoprotein, HCG and estriol).
High levels of these markers can
indicate Down syndrome, but these are screening tests and can return a false
positive (the quad screen is thought to be more accurate) if you’re further
along in your pregnancy than previously thought. If you’re found to be high
risk you’ll be advised to have an amniocentisis.
The information in this feature is intended for
educational purposes only. If you have any concerns about your health, the
health of your child or the health of someone you know, please consult with a
doctor or other healthcare professional.
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Last Modified: 20/06/2007
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