Nuchal translucency scan is the earliest scan you can do to check the abnormality of baby. It is performed at from 11 – 14 weeks of gestation and when the Crown–rump length (CRL) is 45-84 mm. Crown–rump length (CRL). CRL can be measured by either transabdominal or transvaginal scan and should be used to estimate gestational age in all cases except for pregnancies conceived via in-vitro fertilization (IVF Pregnancy).
To obtained an accurate measurement of CRL, this measurement should follow standard criteria. The fetus must be positioned horizontally on the screen and should be in a neutral position (neither flexed nor hyperextended. The image should be magnified to the point where the fetal head and thorax occupy the whole screen. Calipers should be placed at the endpoints of the crown and rump, which need to be clearly visible.
Nuchal Translucency (NT) is the most powerful screening tool to identify fetuses with major aneuploidies to which the common trisomy is Down syndrome (Trisomy 21. This scan helps to detect and congenital malformations especially the cardiac anomaly.
NT is seen as a collection of fluid under the skin in ultrasound and the measurement taken at the back of fetal neck in midsagittal plane of fetal face. At this midsagittal plane, the tip of the nose, nasal bone as well as maxilla should be seen. Research shows thickened NT which more than 3.5 mm linked to increase risk of aneuploidy.
As technology advances and with the vast experience and skill of the sonographer, we can perform more detailed assessments of fetal structures as we shouldn’t restricted to only fetal CRL and NT measurements. These are few structures we can assess at this gestational week, the four-chamber view of fetal heart with color Doppler, fetal abdomen showing fluid-filled stomach in the left side and fetal bladder.
We can also well assess the cord insertion, intact anterior abdominal, overlying skin covering the spine till the coccygeal region, and ossification of the vertebral bodies. The bilateral upper and lower limbs should be seen at this stage.
The NT scan results will show if your baby has a higher or lower risk of chromosomal abnormalities. Keep in mind that this is a screening test, not a diagnostic test. If the results show a high risk, it doesn’t mean your baby definitely has a condition. Your healthcare provider will explain the results and discuss what they signify, as well as your options if further diagnostic tests are suggested, such as CVS or amniocentesis. Many parents with a high-risk NT result ultimately have healthy babies, so keep that in mind.
Overall, Nuchal translucency scan is a valuable scan to check the risk of aneuploidy and fetal structural abnormalities at early stage. By detecting fetal abnormalities earlier in the first trimester improves outcomes by enabling timely interventions, close monitoring and planning, providing accurate information for decision-making, and supporting parents in preparing for the arrival of their baby.