A nuchal translucency ultrasound is commonly used as a screening test to identify pregnancies 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 three things: 1) maternal (the mother’s) age; 2) high-resolution ultrasound assessment of fetal nuchal translucency; and 3) the levels of two proteins (free-BhCG and PAPP-A) in the mother’s blood. The blood test should also be ordered by your doctor to complete the screening test. These three things are used to calculate risk factors of your baby having specific chromosomal abnormalities. Trisomy 21 is the most common and well-known abnormality, often referred to as Down Syndrome.

It is important the study is done during an exact stage of your pregnancy; between 11 weeks to 13 weeks 6 days. During this time, the fetus measures between 45mm and 84mm. The best time to have this examination done is at 12-13 weeks when the fetal size and position make the measurements more accurate and achievable.

A normal fetus accumulates fluid (NT) under the skin behind the head and neck between 9 and 14 weeks of development. This fluid accumulation, or NT, tends to be larger in a fetus affected by a chromosomal abnormality. Once the measurements of the NT are taken, a report is sent to the pathology clinic that has done 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 transducer to come into close proximity to the uterus. A transvaginal scan is optional; it is your decision to have that part of the examination.

Transabdominal and transvaginal ultrasound examinations are safe at all stages of pregnancy.

Procedure

Your examination will be done by a sonographer who will introduce themselves and confirm your identity and the procedure you are having. A clear gel is applied to the skin over the abdomen so the ultrasound probe can move easily over the surface of your skin.

Once images have been taken externally over the abdomen, the transvaginal scan may be offered, and you will be asked to empty your bladder and provided with a gown to change into, or given something to cover you from the waist down. 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 lubricated with gel before being inserted into your vagina and then moved gently to get images of the fetus. This part of the examination generally takes 10-15 minutes. If the examination is causing excessive discomfort or you wish the examination to end, please tell 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 as early in the pregnancy as possible, so that the procedure can be done when you are 12-13 weeks pregnant.

If possible, please wear comfortable, loose-fitting clothing that allows easy access to the area that is being imaged. Two-piece clothing is ideal (separate upper/lower garments).

Transabdominal: You will need a full bladder.  Drink one litre of water one hour before your appointment and do not empty your bladder (do not go to the toilet). Distension of your bladder provides a window to view your pelvic organs and compresses bowel out of the way. Your bladder does not need to be so full that it causes you pain or distress; if this is the case, please tell reception staff on arrival, and they will talk to you about your options.

Transvaginal: Imaging is done with an empty bladder which most women find more comfortable.

Preparation details for your examination will be confirmed when you make your appointment.

Duration

Approximately 30 – 40 minutes.

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