S
S
S
R
R
R
F
F
F
6
6
6
1
1
1
8
8
8
B
B
B
6
6
6
U
U
U
s
s
s
e
e
e
r
r
r
’
’
’
s
s
s
M
M
M
a
a
a
n
n
n
u
u
u
a
a
a
l
l
l
～36～
heart signal can be obtained through the fetal back. See the Fig.8-1 as below.
During parturition, the fetal heart moves downward as the labor progresses. It is
recommended to move the transducer along with the fetus.
Fig. 8-1 Positioning Ultrasound Transducer (single fetus)
8.2.3 Acquiring Fetal Heart Signal
Apply a certain amount of acoustic gel on the underside of the transducer and move it slowly around the
fetus site. Find at least 2 or 3 sites, and choose the one where the clearest, most sonorous and steady fetal
heart sound is heard.
8.2.4 Fixing the Transducer
Wrap the abdomen with the belt over the transducer. Fix the transducer by pushing its buckle through the
overlapping section of the belt.
Make sure the belt fits the patient snugly but comfortably. Meanwhile, fetus heart beat sound is heard; the
FHR trace and numeric are displayed. During long-time monitoring, the gel may dry out as the transducer
moves around. Add more gel in time if it is inadequate.
8.2.5 Confirming that the Fetus is the Signal Source
Ultrasound Doppler technology is utilized to observe the fetal heart rate externally, there are possibilities that
maternal heart rate signal is mistaken for FHR signal. It is highly recommended to confirm that the fetus is
the signal source continuously. You can feel the maternal pulse at the same time.
If the maternal heart signal is misidentified as the fetal heart signal, Repositioning of the transducer is
needed.
NOTE:
1) Do not mistake the high maternal heart rate for fetal heart rate. The fetal pulse can be distinguished from
the maternal pulse by feeling the mother’s pulse during the examination.
2) The best quality records will only be obtained if the probe is placed in the optimum position. Positions
with strong placental sounds or umbilical blood flow sound should be avoided.
3) If the fetus is in the cephalic presentation and the mother is supine, the clearest heart sound will
normally be found on the midline below the umbilicus. During monitoring, the patient’s prolonged lying
in the supine position should be avoided owing to the possibility of supine hypotension. Sitting up or
lateral positions are preferable and may be more comfortable.
4) It is impossible to examine FHR unless a clear fetal heart signal is detected.
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