Fetal Monitoring Equipment

Tocodynamometer

The second component of a fetal monitor is the tocodynamometer. This device measures the relative strength, rate, and duration of uterine contractions. It is basically a ring-style pressure transducer attached to the maternal abdomen via a belt that maintains tight continuous contact with the abdomen. The transducer contains a plunger that is depressed when the uterus changes its rigidity and shape with each contraction. This depression changes the voltage of the current associated with the plunger and is proportional to the strength of the contraction. While the transducer can monitor the activity of the uterus (frequency and relative strength of contraction), it cannot determine the absolute intrauterine pressure. The sensitivity of the transducer is affected by factors such as maternal obesity and premature gestational age and therefore the duration of the contraction may vary depending on that sensitivity. Its advantages are that it is non-invasive and can be used when membranes are intact. An internal uterine pressure transducer is also available if more accurate measurements of uterine activityare desired. This consists of a catheter with a built-in strain gauge that is inserted trans-cervically after membranes are ruptured. It is easier to use and requires less nursing attention.

Toco Transducer

   The goal of monitoring is to maintain adequate, accurate, and continuous fetal cardiac heart rate and uterine activity while ensuring maternal comfort.  While external devices are less invasive, they may not be as accurate.  When more accurate assessment of fetal heart rate and contraction pattern is desired, internal monitoring may be indicated.

Internal Uterine Pressure Transducer

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