A fetal doppler is one type of fetal monitoring. The fetal heart doppler is a non-invasive diagnostic instrument used to detect and measure the fetal heart rate. A fetal heart doppler measures the fetal heart rate by emitting and receiving continuous ultrasonic sound waves and emitting the change or shift in pitch frequency of these sound waves. This is called the Doppler Effect and was discovered by Austrian mathematician and physicist, Christian Doppler (1803-53). Each fetal heart monitor uses a transducer or probe of varying MGHZ (millions of cycles per second), usually 2 or 3, containing piezoelectric crystals which send short sound pulses into the directed area of the body. Every time one of these sound waves is sent the transducer (probe) pauses briefly and listens for the returning echo at which time the fetal heart doppler determines the depth and direction of each returning sound wave and converts the signal into the fetal heartbeat you hear. This heartbeat is not your baby's actual heartbeat but a reproduction.
This is a special type of stethoscope used for listening to a baby. There are many types of fetoscopes available, and a regular stethoscope works as well. This can usually be used after about 30 weeks.
Fetal Heart Doppler
This is a handheld ultrasound device that transmits the sounds of the baby's heartbeat either through a speaker or into ear pieces that are attached. Fetal heart dopplers can usually pick up the fetal heartbeat after 8 weeks gestation.
Electronic Fetal Monitoring
This is an ultrasound device used during labor and birth, or during certain testing (non-stress test, contraction stress test, etc.) to record the baby's heart rate, and sometimes mother's contractions. It can be used intermittently or continuously.
Internal Fetal Monitoring
It is an internal monitoring with an electrode attached to the baby's head to record heart tones, and a pressure catheter to record contractions. This is also used during labor and birth, however, it is not used intermittently.
It is a lot like the regular Electronic Fetal Monitoring, however, one can maintain mobility.