MODEL RELEASED. Foetal doppler ultrasound. Midwife checking the health of a foetus using a portable foetal doppler ultrasound scanner. The transducer, held against the pregnant woman's abdomen, emits high frequency sound waves. If the waves hit a moving object the frequency of their echoes will be altered. This allows the speed of blood flow or the foetal heart rate to be measured. Doppler ultrasound is used routinely during antenatal check-ups. This is a Fetal Dopplex scanner.