Doppler fetal monitor
Encyclopedia
Invented in 1958 by Dr. Edward H. Hon a Doppler fetal monitor or Doppler fetal heart rate monitor is a hand-held ultrasound
transducer used to detect the heart beat
of a fetus
for prenatal care
. It uses the Doppler effect
to provide an audible simulation of the heart beat. Some models also display the heart rate
in beats per minute. Use of this monitor is sometimes known as Doppler auscultation. Doppler fetal monitors are commonly referred to simply as "Dopplers".
Doppler fetal monitors provide information about the fetus similar that provided by a fetal stethoscope. 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.
Originally intended for use by health care professionals, this device is becoming popular for personal use.
The fetal heart begins to beat at approximately the same rate as the mother's, which is typically 80 to 85 bpm. The approximate fetal heart rate for weeks 5 to 9 (assuming a starting rate of 80):
At this point, the fetal heart rate begins to decrease, and generally falls within the range of 120 to 160 bpm by week 12.
The generic use of the word "Sonicaid" for Doppler fetal monitors comes from the products of the UK company Sonicaid 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.
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
transducer used to detect the heart beat
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...
of a fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
for prenatal care
Prenatal care
Prenatal care refers to the medical and nursing care recommended for women before and during pregnancy. The aim of good prenatal care is to detect any potential problems early, to prevent them if possible , and to direct the woman to appropriate specialists, hospitals, etc...
. It uses the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
to provide an audible simulation of the heart beat. Some models also display the heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
in beats per minute. Use of this monitor is sometimes known as Doppler auscultation. Doppler fetal monitors are commonly referred to simply as "Dopplers".
Doppler fetal monitors provide information about the fetus similar that provided by a fetal stethoscope. 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.
Originally intended for use by health care professionals, this device is becoming popular for personal use.
Fetal heart rates
Starting at week 5 the fetal heart rate accelerates by 3.3 bpm per day for the next month.The fetal heart begins to beat at approximately the same rate as the mother's, which is typically 80 to 85 bpm. The approximate fetal heart rate for weeks 5 to 9 (assuming a starting rate of 80):
- Week 5 starts at 80 and ends at 103 bpm
- Week 6 starts at 103 and ends at 126 bpm
- Week 7 starts at 126 and ends at 149 bpm
- Week 8 starts at 149 and ends at 172 bpm
- At week 9 the fetal heartbeat tends to beat within a range of 155 to 195 bpm.
At this point, the fetal heart rate begins to decrease, and generally falls within the range of 120 to 160 bpm by week 12.
Types of Dopplers
Dopplers for home or hospital use differ in the following ways:- Manufacturer: popular manufacturers are Nicolet, Huntleigh, Summit Doppler, EchoHeart, Ultrasound Technologies (Seward / Wakeling), Parks Medical Electronics (as Obstetrical Dopplers),and Sunray.
- Probe type: waterproof or not. Waterproof probes are used for water birthWater birthWater birth is a method of giving birth, which involves immersion in warm water. The immersion can mean giving birth to the infant in the water or using it as a tool during the labor process. Proponents believe that this method is safe and provides many benefits for both mother and infant,...
s. - Frequency: 2- or 3-MHz 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 gestationGestationGestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
). A 2-MHz probe is recommended for pregnant women who are overweight. A new 5-MHz EchoHeart Transvaginal Fetal Doppler Probe 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; for others the fetal heart rate must be counted and timed by the practitioner.
The generic use of the word "Sonicaid" for Doppler fetal monitors comes from the products of the UK company Sonicaid 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.
See also
- Ultrasonic sensorUltrasonic sensorUltrasonic sensors work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor...
- UltrasoundUltrasoundUltrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
- Cardiotocograph
- Nonstress testNonstress testA nonstress test is a screening test used in pregnancy. A cardiotocograph is used to monitor the fetal heart rate.-Premise:The premise of the NST is that a well-oxygenated, non-acidemic fetus will spontaneously have temporary increases in the fetal heart rate...
- AuscultationAuscultationAuscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...