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Foetus. Coloured 3-D ultrasound scan of an eight- week-old foetus in the uterus. A developing embryo is first called a foetus after eight weeks. At this time, the foetus measures about 2.5 centimetres in length. All of the bodily organs have developed and fingers and toes are appearing on the paddle-like limbs. 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. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR NAJEEB LAYYOUS)