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Doppler fetal monitor

Invented in 1958 by Dr. Edward H. Hon[1] 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. A common name for the device is simply "Doppler;" plural is "Dopplers."

A Doppler fetal monitor provides information about the fetus similar to the information a fetal stethoscope provides. One advantage of the Doppler fetal monitor over an acoustic (not electronic) fetal stethoscope is the audio output, which allows people other than the user to listen to the heartbeat. One disadvantage is the greater complexity and cost, and 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 will accelerate at a rate of 3.3 beats per day for the next month.

The fetal heart begins to beat at approximately the same rate as the mothers, which is 80 to 85 bpm. Below illustrates 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.

The fetal heart rate will begin to decrease and generally will fall within the range of 120 to 160 bpm by week 12.[2]

Gender prediction

Evidence indicates that there is no relationship between fetal heart rate and fetus gender,[2] thus fetal heart rate cannot be used as a reliable predictor of the sex of a fetus.

Types of Dopplers

Dopplers for home or hospital use differ in the following ways:

  • Manufacturer - popular manufacturers are Nicolet, Huntleigh, Summit Doppler.
  • Probe type - waterproof or not. Waterproof probes are used for (under) water births.
  • Frequency - 2 or 3 MHz probes. Most practitioners can find the heart rate with either a 2 or 3 MHz probe. A 3 MHz probe is recommended to detect a heart rate in early pregnancy (8–10 weeks gestation). A 2 MHz probe is recommended for women who are pregnant and overweight.
  • 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 use of "Sonicaid" as an everyday term for a Doppler fetal monitor originated through the products of Sonicaid Ltd, a company located in West Sussex in the UK. The 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


  1. ^ Roger K. Freeman, Thomas J. Garite, Michael P. Nageotte, Fetal Heart Rate Monitoring Third Edition, 2003, p. 3. "The earliest preliminary report of FHR monitoring came in 1958 from Edward Hon, MD,... via fetal ECG monitor on the maternal abdomen." Google Books citation
  2. ^ a b [1]


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