A Nuchal Translucency (NT) ultrasound scan provides an opportunity to assess the anatomy of the baby and is used as a screening test to identify pregnancies at an increased risk of a chromosomal abnormality.
The NT scan is performed between 12 weeks 2 days and 13 weeks 4 days (in the first trimester of pregnancy).
The Nuchal Translucency scan consists of high-resolution ultrasound to measure the thickness of the baby’s nuchal fold. This information along with maternal age and maternal serum analyte levels (BhCG and PAPP A from blood test) are put into a risk calculation package which generates a risk factor of your baby having one of the three most common chromosomal abnormalities. Normal fetuses accumulate fluid under the skin behind the head and neck (known as nuchal translucency) between 9 and 14 weeks of pregnancy. The nuchal translucency tends to be larger in a fetus affected by a chromosome abnormality, such as down syndrome, and it can be compared with what is expected for a fetus of the same size (NT Normal Range).
Before your scan
Ideally, please book your appointment as early in the pregnancy as possible, so that the procedure can be done during the suggested period. You can use our Pregnancy Scan Calculator to help with your scan dates.
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).
Please empty your bladder two hours before the examination time. Then slowly drink 600ml of water to fill your bladder and keep it full for your examination.
As part of the test involves combining the ultrasound findings with the maternal blood biochemistry, please take your maternal serum screening blood test form to any pathology company at least 4 days before your ultrasound appointment. We can then access these results at the time of your ultrasound. This can be done from 9 weeks – 13 weeks and 6 days.
When you visit Adelaide Women’s Imaging (AWI) for a Nuchal Translucency scan you will be greeted by one of our friendly reception staff. A sonographer will then collect you from the waiting room and take you to the ultrasound room. The sonographer will perform an ultrasound of the abdomen (transabdominal ultrasound) detailing the fetal anatomy and maternal pelvic anatomy.
Occasionally, the scan may need to be performed through the vagina (transvaginal imaging). Transvaginal ultrasound involves inserting a thin transducer (ultrasound probe slightly thicker than a tampon) into the vagina to get more detailed images as the transducer is closer to the pelvic organs. The transducer is lubricated with gel before insertion into the vagina. There is no risk of infection with transvaginal scanning as the transducer is thoroughly disinfected and covered with a protective cover prior to scanning. Transvaginal ultrasound can improve the accuracy of diagnosis and greater detail may be obtained of the fetal anatomy.
Once the necessary images have been taken, the sonographer will ask you some questions relating to your pregnancy which will add to the risk calculation. You will then be asked to wait in our counselling room where the AWI Doctor will discuss the risk results with you. A detailed report will also be sent to your referring Doctor.
Duration of Scan
Approximately 40 minutes.
Frequently Asked Questions
What happens to the nuchal translucency later in the pregnancy?
In most patients, this disappears and is not visible at the routine 18-20-week ultrasound. This explains why it is important that the scan be performed around 11-14 weeks. There is a narrow window of opportunity when this ultrasound marker of chromosomal abnormality is clear.
What is the risk of the scan?
Transabdominal and transvaginal ultrasound examinations are a safe investigation at all stages of pregnancy.