Antenatal Ultrasound | 20 Week Scans | Private Ultrasound Clinics

More Antenatal Information

Will the scan show my baby’s sex?

By 20 weeks your baby’s sex is often clear, but not all hospitals will tell you. If you want to know, check with your midwife about hospital policy.

Nuchal Translucency Scan

What is Nuchal Translucency?

This is a collection of fluid under the skin at the back of a baby’s neck at 10-14 weeks that can be measured using ultrasound. All babies have some fluid, but in many babies with Down’s syndrome, the nuchal translucency (NT) is increased.

An NT scan is a method of assessing whether your baby is likely to have Down’s syndrome. It is a screening test. A screening test can only estimate the risk of your baby having Down’s, as opposed to a diagnostic test, such as CVS or amniocentesis, which will give you a definite diagnosis (but also carries a small risk of miscarriage).

The NT scan cant tell for certain whether your baby is affected. However, it can help you decide whether or not to have a diagnostic test.

When can I have the test?

NT scans are usually performed from 11 to 13 weeks and 6 days of pregnancy. Before 11 weeks the scan is technically difficult because the baby is so tiny and, after 14 weeks excess fluid may be absorbed by the baby’s developing lymphatic system.

How is it done?

The main part of the test involves an ultrasound scan. The scan is usually done through the tummy, but depending on the position of your baby and your womb, sometimes it is necessary to perform a vaginal scan, which will give better views. There is no risk to you or your baby and it should not be too uncomfortable.

To accurately date your pregnancy, the sonographer will measure your body from the top of its head to the bottom of the spine. She will then measure the width of the NT. The skin will appear as a white line, and the fluid under the skin will look black. Your baby fits nicely on the screen, at this stage, and you will be able to see the head and spine, limbs, hands and feet. Some major abnormalities may be excluded at this scan, but it is recommended you also have a detailed scan at 20 weeks.

What is a normal measurement?

An NT measurement of up to 2.0mm is normal at about 11 weeks, and up to about 2.8mm by 13 weeks and 6 days. This is because the NT normally grows in proportion to the growth of the baby. A baby with a normal NT of 1.3mm will be classed as low risk. If the NT is increased, it does not mean that there will definitely by a problem. Some normal babies will have increased fluid. A baby with an NT of 2.9mm, which is the upper limit of the normal range, will have a higher risk factor than the baby with the NT of 1.3mm. 90% of baby’s with a measurement between 2.5mm and 3.5mm will be completely normal. As the NT increases, so does the risk. A baby with an NT of 6mm and will be very high risk for Down’s, as well as other chromosomal and genetic syndromes and heart problems. Fortunately, not many babies have as much fluid as this.