The 12-week scan, also known as the nuchal translucency (NT) scan, is an ultrasound performed in the first trimester between 11.5 weeks and 13 weeks, six days. The main purpose of this scan is to screen for chromosomal abnormalities such as Downs syndrome. During the scan, the thickness of fluid behind the baby’s neck (nuchal translucency thickness) is measured, and possible structural anomalies are evaluated. The scan can also accurately date the pregnancy and diagnose multiple pregnancies. However, it is important to note that while some major abnormalities can be visible at 12 weeks, it is much better to have an ultrasound examination at 20-22 weeks as well to exclude structural abnormalities as far as possible. If a chromosomal abnormality is suspected, further testing such as a CVS or amniocentesis may be recommended.