What is a fetal doppler?
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.
Other Types of Fetal Heart Monitoring

Fetoscope 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.

Telemetry Monitoring It is a lot like the regular Electronic Fetal Monitoring, however, one can maintain mobility

What should my baby's heart rate be?
Fetal Sounds

A galloping horse is what your baby's heartbeat will sound like and will be about twice as fast as the mother's heart rate. An average normal fetal heart rate is between 120-180 BPM (Beats Per Minute). Where as an average adult heart rate at rest is between 60-100 BPM.

Maternal Sounds You may also hear sounds of your own heart or blood flow. A major artery runs through your abdomen and the swish of your blood through it is sometimes picked up by the fetal doppler. This sound is heard by the baby later in pregnancy and has been recorded and used to calm upset babies after birth.

Placental Sounds The blood flow becomes steadier as it flows through the placenta and has a distinctive sound like wind blowing through the trees.

Instrument Noise The fetal doppler itself may have some background noise, static, popping etc. When the fetal doppler probe is moved on the abdomen, louder popping noises may result. Sometimes, the movements of your baby in later pregnancy also produce louder noises. Ultrasound gel use is integral on cutting down on much of the static produced when positioning the fetal dopplers trasducer during an exam

How do I use my fetal doppler? The best way to begin an exam is to be lying down exposing the abdomen, although it may be possible to find the heart rate in a sitting or standing position. Apply a generous amount of ultrasound gel to the fetal doppler probe. Early in pregnancy the best technique is to begin with the transducer (probe) on the midline of the abdomen (above the pubic line) aiming downward behind the pubic bone. The probe should then be angled slowly in search for the fetal heart rate. Be patient, early in pregnancy the size of the fetal heart is so small and the sound so faint it can be very easy to pass over and miss the sounds. A 2mghz probe is best for early detection, standard on Huntleigh FD1+ and D920. A full bladder can make it easier to find the heartbeat. Try to keep from dragging the probe around as it will only increase static and make it more difficult to find the heartbeat FAQ Main

How often can I use my fetal doppler?
The Food and Drug Administration regulates ultrasound in the United States and has cleared it for "continuous use". As there is no consensus on what this means or how often you should use your fetal doppler it is commonly recommended that like everything in life prudence is the best policy. When using your fetal doppler it is suggested that you use it in short intervals, infrequently, and following the first trimester.
As a general rule an exam with a fetal doppler should never last longer than 10 minutes. If you don't find the heartbeat in this period of time, take a break. If your concerned contact your health care provider. If not, try again in a few days.
The AIUM (American Institute of Ultrasound in Medicine) suggests "prudent" use FAQ Main

How often can I use my fetal doppler?
The Food and Drug Administration regulates ultrasound in the United States and has cleared it for "continuous use". As there is no consensus on what this means or how often you should use your fetal doppler it is commonly recommended that like everything in life prudence is the best policy. When using your fetal doppler it is suggested that you use it in short intervals, infrequently, and following the first trimester.
As a general rule an exam with a fetal doppler should never last longer than 10 minutes. If you don't find the heartbeat in this period of time, take a break. If your concerned contact your health care provider. If not, try again in a few days.
The AIUM (American Institute of Ultrasound in Medicine) suggests "prudent" use FAQ Main

How do I know I'm hearing my baby's heartbeat and not mine?
The easiest and most conclusive way to decipher your heartbeat from your baby's is by the heart rate or BPM (beats per minute). Your baby's heart rate will be between 120 & 180 BPM. This is considered the normal range of a fetal heart rate. Conversely, your heart rate will be much less 60-100 BPM. Early in pregnancy its normal for the fetal heart rate to vary within a reasonable range. As your pregnancy progresses and your baby grows the heart rate will become more static. Also be aware that like adults your baby's heart rate will vary depending on activity level. If you have further questions or concerns about your baby's heart rate contact your health care provider. FAQ Main

Why do I need ultrasound gel?
Ultrasound gel is imperative when doing and exam with a fetal doppler. Ultrasound gel is specially formulated to act as a coupling agent and reduce static that is often caused when using a fetal doppler. To get uptimal use and sound out of a fetal doppler monitor use plenty of gel. Do not use colored gels or lotions. Any oil based substance used with a fetal doppler will cause excess static and can damage the doppler probe. Since the probe is one of the most integral parts of the doppler system they can run upwards of $300 to replace. Use only ultrasound gel FAQ Main

What's the difference between a 2MHz and 3MHz fetal doppler probe?
All baby heart monitors designed for fetal heartbeat monitoring is equipped with either a 2 or 3mghz probe. With a 2mghz probe the beam is narrow and direct which helps it penetrate deeper (3-5cm compared to 1-2cm) and find the fetal heartbeat earlier than 3mghz dopplers.

• The higher the frequency, the shorter in duration is the period and the shorter is the wavelength
• The lower the frequency, the longer in duration is the period and the longer is the wavelength