A nuchal translucency ultrasound is a specialised examination commonly used as a screening test to identify those pregnancies that are at an increased risk of a chromosomal abnormality.
A Nuchal Translucency ultrasound (NT) is often referred to as combined first trimester screening in that it correlates maternal age with high-resolution ultrasound assessment of fetal NT and the levels of two proteins (free-BhCG and PAPP-A) in a pregnant woman’s blood. A blood test should also be ordered by your doctor to complete the screening test. This data is used to calculate risk factors of your baby having specific chromosomal abnormalities. Trisomy 21 is the most common and well known, often referred to as Down Syndrome.
It is very important that the study is done during an exact stage of your pregnancy; between 11weeks to 13 week 6 days. This correlates to the fetus measuring being 45 and 84mm. The best time to perform this examination is at 12-13 weeks when the fetal size and position makes the measurements more accurate and achievable.
Normal fetuses accumulate fluid (NT) under the skin behind the head and neck between 9 and 14 weeks of pregnancy. The NT tends to be larger in a fetus affected by a chromosomal abnormality, such as Down Syndrome. Once these measurements are concluded and a report finalised, this data is sent to the body that has performed your blood test. In South Australia this is commonly completed at the South Australian Maternal Serum Antenatal Screening program (SAMSAS) or by a private pathology provider. Your referring doctor will then receive a risk analysis for your pregnancy.
In most cases the ultrasound will be performed transabdominally but there are some situations where an internal or transvaginal ultrasound may be necessary. Transvaginal ultrasound involves placing a thin transducer (slightly thicker than a tampon) into the vagina. The transvaginal ultrasound provides extra detail as it allows the ultrasound probe to come into close proximity to the uterus. A transvaginal scan is optional for all patients and it is your decision whether to proceed with that part of the examination.
Transabdominal and transvaginal ultrasound examinations are safe investigations at all stages of pregnancy.
About this Ultrasound
Your examination will be performed by a sonographer. Upon being taken into the examination room the sonographer will introduce themselves, confirm your identity and examination. A clear gel is applied to the skin over the area to be examined. The ultrasound probe is moved over the surface to study the structures below.
Once images have been obtained externally over the abdomen, the transvaginal scan may be offered and you will be asked to empty your bladder and change in to a gown or be appropriately covered. The transvaginal transducer is disinfected before use and a protective cover is placed over the transducer each time it is used, so there is no risk of infection. The probe is then lubricated with gel prior to insertion into the vagina, and then moved gently to visualise the fetus. This part of the examination generally takes 10-15 minutes. If at any time the examination is causing excessive discomfort or you wish the examination to end, please advise the sonographer immediately.
If appropriate and available, you will be able to obtain some images at the end of your examination in accordance with the Dr Jones & Partners multimedia policy.
Before your Scan
Ideally book your appointment when you will be 12-13 weeks.
It is a good idea to wear comfortable, loose fitting clothing that allows easy access to the area that is being imaged, so two piece clothing is ideal (separate upper/lower garments).
Transabdominal: A full bladder is required. Drink 500mL of water finishing one hour prior to your appointment and do not empty your bladder. Distension of your bladder provides a window to view your pelvic organs and compresses bowel out of the way. Your bladder need not be overly full that it causes you pain or distress; please advise reception staff on arrival if this is the case and you will be advised of your options.
Transvaginal: Imaging is performed with an empty bladder and as a result many women may find it more comfortable.
Preparation details for your examination will be confirmed when you make your appointment.
Approximately 30 – 40 minutes.
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