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Fetal Dopplers

by Dr. John McGarry, MB, ChB, DRCOG, MRCOG, FRCOG (1986), MFFP (1993)

I first used small sized fetal Doppler listening devices in about 1970 and have continued to use them throughout a long professional career as an obstetric consultant in both academic and non-academic units. During the last nearly 4 decades I have tried to keep up with all the contemporary medical literature concerning the use of such devices. Throughout all this time my main concern had been concentrated on whether the careful use of such devices has been totally safe for both the mother and the unborn baby (or babies!)

The most significant and authoritative document that has appeared over the years on the safety of these devices and similar and more complex ultrasound machines is "The Safety of Diagnostic Ultrasound" by Professor P N T Wells, a report of a British Institute of Radiology Working Group published in 1987. Also involved with this publication were representatives from the Royal College of Obstetricians and Gynaecologists.

To summarise, and including data from subsequent reports over the years, the conclusions were, and have remained so, that provided the investigation is used over fairly brief periods of time and not with excessively frequent use, quoting from the above report (page 27) "It is concluded that ultrasound probably has no proven hazard to the patient but that to date there is insufficient research to make a definitive statement".

Since that report there have been no reports that simple hand held Doppler devices if used with care can cause any harm to the fetus.

So what should you do or not do with your machine?

1. Tell your obstetric attendants that you are using it.
2. Try to listen to the baby about once a week, and certainly ideally no more than every 2-3 days.
3. Try to listen for no longer than 3-4 minutes, and if you are having early (Braxton-Hicks) contractions, use the machine before, during and after a contraction.
4. The average (mean) fetal heart rate is 140 beats per minute, with a range of about 120-160; the rate often falling in the middle of a contraction.
5. If in the unlikely event of picking up a fetal heart which is outside the above range tell your medical attendants as soon as possible, but try not to panic. The chances are that there will turn out to be nothing wrong in over 99% of cases when an expert "rescans" your baby.
6. It can be useful, if, each time you use the machine, you write down the time of day, the date and the observed heart rate. Take this recording with you to your next clinic appointment.
7. Remember that the most common error with these devices is to mistakenly listen to your own heart rate (around 72 beats per minute) because you are aiming at the maternal blood vessels and missing the baby's.

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