A Doppler fetal monitor is a hand-held

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

transducer used to detect the

fetal heartbeat Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is t ...

for

prenatal care Prenatal care, also known as antenatal care, is a type of preventive healthcare. It is provided in the form of medical checkups, consisting of recommendations on managing a healthy lifestyle and the provision of medical information such as materna ...

. It uses the

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

to provide an audible simulation of the heart beat. Some models also display the

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

in beats per minute (BPM). Use of this monitor is sometimes known as Doppler

auscultation Auscultation (based on the Latin verb ''auscultare'' "to listen") is listening to the internal sounds of the body, usually using a stethoscope. Auscultation is performed for the purposes of examining the circulatory and respiratory systems (hea ...

. The Doppler fetal monitor is commonly referred to simply as a ''Doppler'' or ''fetal Doppler''. It may be classified as a form of

Doppler ultrasonography Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of ...

(although usually not technically

-graphy The English suffix -graphy means a "field of study" or related to "writing" a book, and is an anglicization of the French ''-graphie'' inherited from the Latin ''-graphia'', which is a transliterated direct borrowing from Greek. Arts * Cartogr ...

but rather sound-generating). Doppler fetal monitors provide information about the fetus similar to that provided by a

fetal stethoscope A Pinard horn is a type of stethoscope used to listen to the heart rate of a fetus during pregnancy. It is a hollow horn, often made of wood or metal, about long. It functions similarly to an ear trumpet by amplifying sound. The user holds the w ...

. One advantage of the Doppler fetal monitor over a (purely acoustic) fetal stethoscope is the electronic audio output, which allows people other than the user to hear the heartbeat. One disadvantage is the greater complexity and cost and the lower reliability of an electronic device. The device was invented in 1958 by Dr. Edward H. Hon, Originally intended for use by health care professionals, this device is becoming popular for personal use.

Types

Dopplers for home or hospital use differ in the following ways: *Manufacturer: popular manufacturers Baby Doppler, Sonoline, Ultrasound Technologies, Newman Medical, Nicolet (purchased by Natus), Arjo-Huntleigh, and Summit Doppler (now Cooper Surgical). *Probe type: waterproof or not. Waterproof probes are used for

water birth Water birth is labor and sometimes delivery that occurs in water, usually a birthing pool. The American College of Obstetricians and Gynecologists does not recommend birthing in water as the safety has not been determined. Proponents believe ch ...

s. *Probe frequency: 2-

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

or 3-

probes. Most practitioners can find the heart rate with either probe. A 3-MHz probe is recommended to detect a heart rate in early pregnancy (8–10 weeks

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

). A 2-MHz probe is recommended for pregnant women who are overweight. The newer EchoHeart 5-MHz transvaginal probes aids in the detection of fetal heart tones (FHT) early in pregnancy (6–8 weeks) and for patients who have a retroverted uterus or throughout pregnancy for FHT detection for women who are obese. *Heart rate display: some Dopplers automatically display the heart rate on a built-in LCD; for others the fetal heart rate must be counted and timed by the practitioner. A major advantage of being able to record and share the recording is that it can be emailed to a healthcare professional to be checked if there are any concerns about whether or not it is the fetus's heart rate and whether or not is normal. Typically, they work from about 12 weeks. In response to increasing home usage of clinical fetal doppler systems, the FDA issued a formal statement recommending against at-home use. Fetal dopplers using 2-3MHz ultrasound are prescription devices designed and developed for use by licensed and trained health care professionals. System misuse (duration, angulation) and systems operating outside of intended range can produce thermal and non-thermal effects on fetal tissue, including the possibility for over-heating fetal tissue and introducing mechanical stress on the fetus due to cavitation, radiation force, and acoustic streaming. The use of the word ''Sonicaid'' for Doppler fetal monitors comes from the products of the UK company

Sonicaid Sonicaid Ltd was a medical electronics company headquartered in West Sussex best known for its range of Doppler fetal monitors. The company also developed early ultrasound scanners. The word "Sonicaid" is in generic use for Doppler fetal monitors ...

Ltd. Sonicaid products included the D205/206 portable fetal Dopplers and FM2/3/4 series of fetal monitors. The company was acquired by Oxford Instruments in 1987 to form Oxford Sonicaid.

References

{{DEFAULTSORT:Doppler Fetal Monitor Obstetrics Medical monitoring equipment Midwifery

Types

See also

References