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The nuchal translucency scan combines an ultrasound scan with a blood test to give an approximate risk factor of the baby being diagnosed with a chromosomal abnormality such as Downs Syndrome. 

What are chromosomes?
Chromosomes are the genetic blue print or codes which direct how a fetus will develop.  They also pass certain characteristics from parents to their children.  Abnormalities occur when there are too many, too few, or abnormal chromosomes.

What are the risks of abnormality?
There are several hundred types of chromosome disorder but Down's Syndrome (Trisome 21) is one of the most common and occurs in about 1 in 700 pregnancies.  Down's Syndrome occurs when a baby has an extra chromosome which results in disruption of the normal development, causing birth defects and learning difficulties.

Though the chance of having a baby with Down's Syndrome increases as a woman gets older, more babies with Down's Syndrome are born to younger women because the overall birth rate is higher in this age group.  For this reason, screening tests for women regardless of age have been introduced. 

The blood test
The blood test measures the amount of two proteins called PAPP-A and Free Beta HCG.  These proteins appear naturally in the mother's blood during pregnancy.  A change in the level of these proteins can tell us about abnormalities which may sometimes occur in the baby, for example a high Free Beta HCG and low PAPP-A can indicate Down's Syndrome.

The ultrasound scan
Ultrasound uses sound waves to make a picture of your baby and can show its age and position as well as if you have twins.  During the scan, the Ultrasonographer will measure the amount of fluid behind the neck of the baby, sometimes called the nuchal translucency.  This measurement along with your baby's age, your own age and the results of your blood test will allow us to calculate the individual risk of your baby having a chromosomal abnormality.  You will be given an  image of your baby to keep at the end of your scan.

How do I find out my results?
Your results will be sent to your referring midwife, doctor or consultant with whom you should arrange an appointment to discuss them.  Our Ultrasonographers are unable to discuss any of the results with you.

We always aim to send out results within one working day after your test but you may need to allow time for your surgery to process the results. 

Your risk results
It is important to remember that this test will not say with certainty that your baby has or has not got a chromosomal problem - but it will assess the risk.  Also not all abnormalities will be found by this screening test.

When the risk is assessed as an increased risk, parents may be referred to discuss this with a doctor or midwife.  This result itself does not mean your baby is abnormal, approximately 5% of normal pregnancies will have such a result.  Follow-up tests are needed to explain why the results indicate increased risk and most women (34 out of 35) with these increased risk results go on to have healthy, normal babies.

After discussing the increased risk results with your midwife or doctor, it may be appropriate for follow-up tests to be performed by a specialist.  The specialist will be able to discuss with you the appropriate diagnostic test which is usually CVS (Chorion Villous Sampling).  This test will involve taking fragments from the placenta.  The cells in this tissue are then examined to check the chromosomes of the baby.  The results are usually available within 10 days.  There is a small risk of miscarriage following the CVS which is around 1% and is the same as amniocentesis.

When can I have this test?
You must be between 11 and 14 weeks pregnant. 

What if I am more than 14 weeks pregnant?
If your ultrasound indicates that you are more than 14 weeks pregnant or if you are later than 14 weeks at booking, you cannot have the nuchal translucency and PAPP-A test but may be offered alternative blood testing at 16 weeks by your midwife.  It is therefore essential to book an appointment at the early stage of your pregnancy to achieve the best possible chance of detecting abnormalities.

How do I book an appointment?
Please call the Diagnostic Centre on 020 8936 1202.  You will need to bring with you either a letter of referral from your midwife, consultant or GP, or else have full contact details for them.