The NT scan is usually performed between 11 and 13.6 weeks 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. Nuchal translucency (NT) is the sonographic appearance of a collection of fluid under the skin behind the foetal neck in the first-trimester of pregnancy. The sonographer will perform a transvaginal scan which can pick up a better image of your baby. The NT thickness is measured and this gives the risk or estimate of the baby having Down's syndrome and other conditions. A scan can only indicate the level of risk of your baby having Down's syndrome. To get a definitive 100% answer for chromosome abnormalities including Down syndrome, a prenatal diagnostic test is needed like a blood test to give a more accurate assessment which is also available to perform in our clinic (Verify DNA Test). The nuchal translucency scan is usually advised in first time pregnancies, high-risk pregnancies and in pregnant women who are over 35 years of age.
The full scan will provide the following information:
> Number of foetuses. Determination of chorionicity in twin pregnancy (identical twins) for example can be made early and extra surveillance of these high risk pregnancies can be organized to optimize the outcome.
> Detection of foetal heart movement/rate. Seeing the heart beating is reassuring and confirms that the baby is okay. The heart usually starts beating at about six weeks.
> Determines the gestational age of the foetus. This can be made accurately by measuring the crown-rump length (CRL). It will help in determining the expected date of delivery (EDD).
> Foetus anatomy:
o The shape and structure of your baby's head. It is possible to detect severe brain problems at this stage, but fortunately these are very rare.
o Your baby's abdominal wall, to make sure it covers all the internal organs at the front.
o Your baby's stomach. Your baby swallows some of the amniotic fluid that he lies in, which is seen in his stomach as a black bubble.
o Your baby's kidneys. The doctor will check that your baby has two kidneys, and that urine flows freely into his bladder. If your baby's bladder is empty, it should fill up during the scan and be easy to see. Your baby has been passing urine every half an hour or so for some months now!
o Your baby's heart. The top two chambers (atria) and the bottom two chambers (ventricles) should be equal in size. The valves should open and close with each heartbeat.
o Your baby's spine, both along its length and in cross-section, to make sure all the bones align and that the skin covers the spine at the back.
o Your baby's arms, legs, hands and feet. The doctor will look at your baby's fingers and toes, but not count them.
o Full nuchal translucency scan (NT)