Umbilical blood flow. Coloured doppler ultrasound scan showing umbilical blood flow. The foetus is laying across bottom at left. Oxygenated (arterial) blood, which is flowing from mother to foetus, is red. Deoxygenated (venous) blood, which is flowing from foetus to mother, is blue. Maternal blood supplies the foetus with oxygen and nutrients. 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 in pregnancy. This technique allows the determination of the speed of blood flow and other movements.