Nuchal Translucency Scanning

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A nuchal translucency ultrasound scan is performed between 11 and 13+6 weeks of pregnancy. This measures the “Nuchal fold / translucency” an area on the back of your baby’s neck. It is a screening test used to predict the risk of Down’s syndrome and can also be an indicator of other chromosomal abnormalities.
This measurement results can be used alone or in combination with a blood test to calculate a patient’s individual risk. Data is correlated with Fetal Medicine Centre, London.
If your result returns as screen positive, you will be offered an amniocentesis or chorionic villous sampling (CVS) to give you a more definite answer about the presence of foetal abnormality.

Appointments for this scan can be made with our consultant Obstetrician.

 

Nuchal Translucency & The Combined Test – Information for You

What is the combined test?

The combined test is a screening test offered to pregnant women between 11 and 13+6 to identify pregnancies that have a higher chance of being affected with Down’s syndrome.
The test combines information from a scan of the baby and a blood test from you. The scan also called the ‘nuchal scan’ measures the fluid behind the nape of the baby’s neck. All babies have this fluid, but the amount of fluid may be more in babies with Down’s syndrome. The nuchal scan alone can be used as a screening test for Down’s syndrome giving a detection rate of about 69%, but it is more useful when combined with the blood test, this increases the detection rate to 77-80%.
The blood test measures two substances in your blood. These are hormones called PAPP-A (pregnancy associated plasma protein- A) and free β-hCG (β-human chorionic gonadotrophin). In pregnancies with Down’s syndrome, PAPP-A tends to be low. Nuchal translucency (NT) and free β-hCG tend to be raised.
The test also uses information of your age.
The results will be either screen positive or screen negative.

How good is the combined test?

The combined test is a screening test that predicts the chance of your baby having Down’s syndrome. It cannot however tell you if your baby is definitely affected or not. The combined test picks up 84% of babies with Down’s syndrome (more than four out of five). This means that 16% of Down’s babies (less than one in five) are not picked up. The false positive rate for the test is about 2.2% (about two out of 100 tests).

What are the benefits of the combined test?

Some women would like to know if their baby is at high risk of Down’s syndrome early in the pregnancy. The combined test has the advantage of providing a risk estimate in the first trimester.

What does a screen positive result mean?

A screen positive result means that you are in a higher risk group of having a baby with Down’s syndrome. The result is called screen positive if the combined risk is 1 in 150 or more.
If you are screen positive, you will be offered a diagnostic test which could be either chorionic villus sampling (CVS) or amniocentesis.

What does a screen negative result mean?

If the combined test gives a risk estimate of less than 1 in 150, the result is called ‘screen negative’. Although a screen negative result means that you are not at high risk of having a baby with Down’s syndrome, a screen negative result does not rule out the possibility of a pregnancy with Down’s syndrome.

Does the combined test detect all pregnancies with Down’s syndrome?
No. About 8-9 out of 10 cases are detected (called screen positive). About 1-2 out of 10 pregnancies will have a screen negative result and so will be missed out by the combined test.

Does the combined test check for other problems?

The measurements used as part of the combined test can also identify pregnancies at high risk of Edwards’ syndrome (Trisomy 18). This is a rare, but serious condition and affected babies can have a range of severe medical problems. The combined test detects about 6 out of 10 pregnancies with Edwards’ syndrome.

What is a diagnostic test?

A diagnostic test finds out for definite whether your baby has Down’s syndrome or not. These are either chorionic villus sampling (CVS), carried out between 11-14 weeks or amniocentesis, carried out from 16 weeks. However diagnostic tests carry a risk of miscarriage, which is about 1 in 75 for CVS and 1 in 100 for amniocentesis.

If you have difficulty deciding what to do and would like to talk to a health care professional, please call 028 9066 6815 to arrange an appointment.