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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