Nowadays, it is normal for parents to eagerly anticipat
e hearing their baby’s heartbeat around
10 weeks gestation and seeing an ultrasound picture or
sonogram of their baby as early as possible.
Seeing and hearing the baby’s heartbeat is reassurance th
at all is well. Before the 1970’s, diagnostic
ultrasound was not widely available. Doctors and midwi
ves listened to fetal heartbeats with a special
but old fashioned stethoscope called a fetoscope. Som
etimes the parents would be given a turn to
listen to the heartbeat themselves. There were no pict
ures of the baby prior to birth. The advent of
diagnostic ultrasound radically changed access to informat
ion concerning the development of the
unborn baby.
Diagnostic ultrasonography is a cross-sectional and three-d
imensional anatomic and flow
imaging technology using pulse-echo ultrasound. Ultraso
und is usually described as “high frequency
sound waves,” making it seem harmless. Sound that is audib
le to humans is between 20 hertz and 20
kilohertz. Ultrasound is between two and four megahe
rtz, and has been classified as radiation by the
Bureau of Radiological Health (a branch of the Food a
nd Drug Administration). Ultrasound is not
ionizing radiation like x-rays, but it is sound radiation
. Three types of ultrasound diagnostic devices in
use in obstetrics are ultrasound scanning devices, dopplers
and fetal monitors.
Ultrasound scanning devices are used to make the picture or
sonogram of the unborn baby.
The mother lays on an exam table, her belly is uncovered,
and a lubricant applied. Then a sound
emitting device is passed over her abdomen in different d
irections and a sound wave of very high
frequency is radiated through the tissue. Since tissues a
t various distances from the transducer
conduct sound differently, the sound waves are converted int
o a picture as they bounce off the body
parts of mother and baby. This picture is then interpre
ted by a ultrasound technician. A-scan
ultrasound technique produces one or two-dimensional
images and can assess fetal age, weight,
position, placental location, and the gross appearance o
f the fetus. Use of this amplitude has largely
been replaced with the B-scan, which can determine the
size and position of structures via a cross-
sectional image. Real time ultrasound uses high-speed s
canning to allow visualization of moving
structures such as heart and fetal activity. Another ultra
sound device is a cylindrical probe inserted into
the vagina to view pelvic organs. Ultrasound can seemin
gly provide a wealth of information about the
baby and can be used to confirm or rule out problems wh
en prenatal screening detects a concern.
Dopplers or Doptones are the hand held devices that are
used for detecting your baby’s
heartbeat by using ultrasound. The echoes are detected
by a receiver and translated into the “swish-
thump” sounds that are heard when the Doppler is plac
ed on the woman’s belly. Doppler effect
ultrasound measures movement by using continuous wave tra
nsmission and detecting the change in
the frequency of returned signals as a result of movemen
t of the target. Doppler devices expose the
fetus to more powerful ultrasound than imaging ultraso
und exams. One minute of Doppler exposure is
equal to 35 minutes of real time ultrasound. The exte
rnal fetal monitor used during labor and delivery in
the hospital is also using continuous doppler, ultrasoun
d monitoring. Doctors and midwives can use the
old-fashioned fetoscope that simply uses the human ear, t
o listen to and monitor the baby’s heartbeat.
Although diagnostic ultrasound is quite expensive, studie
s show that ultimately ultrasound does
not significantly improve fetal outcomes; it does, howe
ver, increase medical intervention. There is also
the theoretical concern about what happens when sound w
aves strike growing fetal tissues. When
wound waves bombard laboratory tissues at high frequencie
s, they shake up the molecules, heat them,
and produce microscopic gas bubbles in the cell called “ca
vitation.” The effects of heat and cavitation
on fetal cells is an ongoing debate in scientific circles r
aising questions about the overuse of diagnostic
ultrasound when for millenniums, babies have done just
fine without it. If there is a particular concern,
the benefits of having minimal ultrasound exposure may o
utweigh the risks of ultrasound exposure.
Parents should carefully weigh the latest research in
making a decision as to whether they want an
ultrasound “picture” of their baby or the routine use
of the Doppler to monitor the baby’s heart beat. Fo
more information on ultrasound and other pregnancy issue
s check out the website of “Midwifery


Please enter your comment!
Please enter your name here