Foetus's face. Coloured 3-D ultrasound scan of a foetus' face with pursed lips. The foetus' nose is at centre, the mouth is below it and the eyes to either side. This was taken in the third trimester of pregnancy. Ultrasound scanning is a diagnostic technique that sends high-frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure. Foetal ultrasound scanning is routine during pregnancy. 3-D scanning uses computer technology to return more detailed images than conventional 2-D scans.