What is Nuchal Scanning?
Nuchal scanning is an ultrasound scan to help determine the likelihood of Down's Syndrome and other chromosomal abnormalities in unborn babies.
What is Down’s syndrome?
Down’s syndrome is a genetic disorder. In the most common form of Down’s syndrome each of the body’s cells has an extra chromosome (chromosome 21). Down’s syndrome is the most common cause of learning difficulties. Anyone can have a baby with Down’s syndrome; however the risk increases with age. The chance of having a baby with the condition is 1 in 1500 for women 20 years of age, 1 in 900 for women 30 years old and 1 in 100 for women who are 40 years old.
Testing for Down's Syndrome
Parents-to-be can choose to test their unborn babies for Down’s syndrome. A screening test will give an indication of which babies have an increased risk of Down’s syndrome and other chromosomal abnormalities such as Edward’s and Patau syndromes. It does not carry a risk of miscarriage as it is non-invasive but it does not give a definitive answer.
A diagnostic test such as chorionic villus sampling and amniocentesis will give a definitive answer but both carry the risk of miscarriage.
The combined test
Spire Healthcare offers the latest of non-invasive screening tests for Down’s syndrome. The combined test considers both the nuchal translucency ultrasound scan and a blood test from the mother to work out a risk figure.
A Nuchal translucency scan (NT) measures the amount of fluid lying under the skin at the back of the baby’s neck. Babies with Down’s syndrome, heart and other chromosomal abnormalities have an increased amount of fluid here. The scan will additionally provide you with information on multiple pregnancy, it accurately dates your pregnancy, it can exclude major abnormalities and miscarriage at that stage of the pregnancy.
The blood test measures the amount of a hormone and a protein that are found naturally in the mother’s blood. These substances have passed from the baby to the mother.
A computer programme uses the nuchal scan measurement, the size of the baby, the mother’s age and the blood results to work out a risk for Down’s syndrome for the baby.
This combined test allows the screening process to be more accurate and is recommended by the National Screening Committee (NSC) and the Fetal Medicine Foundation (FMF).
Timing of the combined test
The best time to perform this test is between 11 and 14 weeks of gestation. Women who are unsure of their dates are recommended to have a dating scan before the screening test.
Who performs the scan?
The nuchal translucency scan is performed by an obstetrician, gynaecologist or an advanced practitioner in medical diagnostic ultrasound who is certified for nuchal translucency scanning as regulated by the Fetal Medicine Foundation.
What do the results mean?
The results provide you with a risk factor for Down’s syndrome. With this information you can then make an informed decision of whether you are comfortable with the risk factor of if you would like to proceed with an invasive test.
As a guide, if the combined test shows the risk of the baby having Down’s syndrome is relatively high (e.g. one in 100) an invasive test is usually offered.
What to expect
You will have an initial consultation with a Consultant Gynaecologist and Obstetrician.
Before your nuchal scan you may need to drink a pint of water so that you attend with a full bladder. The scan is performed on your tummy. If your baby is in a difficult position an internal scan may be needed. During the scan the pregnancy will be dated, measured and assessed for major physical abnormalities.
If the baby is between 11 and 14 weeks a blood sample will be taken. If the dates are incorrect the screening test will be deferred to the appropriate time. There will be a charge for the dating scan.
The test results will be discussed with you on the day or over the phone and a printed report will be provided. We recommend that you give a copy of the report to your Midwife, GP or Consultant Obstetrician.
If the results show an increased risk you will be offered a further consultation to discuss the results and the next steps.
To have a combined test you can self-refer or ask your GP or midwife for a referral.