A specialist first-trimester ultrasound performed between 11 and 14 weeks of pregnancy to measure the fluid at the back of the baby's neck and assess the risk of chromosomal conditions including Down's syndrome.
The nuchal translucency scan is one of the most important assessments in early pregnancy. Performed between 11 and 14 weeks, it measures the fluid-filled space at the back of the baby's neck — a measurement that, when combined with blood tests, forms the combined first-trimester screening test for Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18), and Patau's syndrome (trisomy 13). Many parents choose a private NT scan to access earlier, more detailed assessment or to receive results in a calm, unhurried environment. Our specialist sonographers at 29 Weymouth Street, Marylebone, perform NT scans to the exacting standards required by the Fetal Medicine Foundation (FMF).
The nuchal translucency (NT) measurement is the thickness of the fluid-filled space at the back of the fetal neck, measured on ultrasound between 11+0 and 13+6 weeks of pregnancy (crown-rump length 45–84mm). An increased NT measurement is associated with a higher risk of chromosomal abnormalities, particularly trisomy 21 (Down's syndrome), trisomy 18 (Edwards' syndrome), and trisomy 13 (Patau's syndrome), as well as certain structural heart defects and other conditions. The NT measurement alone provides a detection rate of approximately 75% for Down's syndrome. When combined with maternal blood tests (PAPP-A and free beta-hCG) as part of the combined first-trimester screening test, the detection rate rises to 90–95%. The scan also assesses fetal anatomy, confirms viability, measures crown-rump length for accurate dating, and checks for the presence of the nasal bone — an additional marker for chromosomal risk.
A moderately full bladder is helpful for the transabdominal scan. Drink 500ml of water 30 minutes before your appointment.
Warm gel is applied to your abdomen and the sonographer begins the assessment, confirming viability, measuring the crown-rump length, and evaluating fetal position.
The sonographer obtains the nuchal translucency measurement in the correct fetal position, following Fetal Medicine Foundation (FMF) standards. Multiple measurements are taken to ensure accuracy.
The nasal bone, fetal anatomy, and other first-trimester markers are assessed. In multiple pregnancies, chorionicity is determined.
The NT measurement and all findings are discussed with you immediately. A written report with measurements and images is provided before you leave.
Your sonographer will explain the NT measurement and all findings with you immediately after the scan. The written report includes the NT measurement, crown-rump length, gestational age, nasal bone assessment, and a summary of the fetal anatomy survey. The NT measurement alone provides an indication of risk, but a definitive risk calculation for Down's syndrome, Edwards' syndrome, and Patau's syndrome requires combination with maternal blood tests (PAPP-A and free beta-hCG) as part of the combined first-trimester screening test. If you have not yet had these blood tests, we can advise on how to access combined screening. An increased NT measurement does not mean your baby has a chromosomal condition — it indicates a higher statistical risk that warrants further discussion with a fetal medicine specialist.
Our HCPC-registered sonographers are available Monday to Saturday. Results discussed immediately, written report within 24 hours.