Background
An intrauterine pressure catheter (IUPC) is a device placed into the amniotic space during labor in order to measure the strength of uterine contractions.
External tocodynamometers are used to measure tension across the abdominal wall and detect only contraction frequency and duration. The appearance of contractions by external monitoring may be affected not only by contraction strength but also by maternal habitus, position, gestational age, and monitor location on the abdomen.
Intrauterine pressure catheters work by directly measuring pressure within the amniotic space using a pressure transducer at the tip of the catheter which allows for quantification of contraction strength. After connection to the appropriate cable, contractions are measured in mm Hg and displayed on the monitor in a graphic fashion (see image below).
With an intrauterine pressure catheter in place, Montevideo units (MVUs) can be calculated to assess for adequacy of labor in cases of suspected labor dystocia or during labor induction. MVUs are calculated by subtracting the baseline uterine pressure from the peak uterine pressure of each contraction in a 10-minute window of time and then taking the sum of these pressures. Two hundred Montevideo units or more is considered adequate for normal labor progression. [1]
Routine use of intrauterine pressure catheters is not recommended. A large randomized trial of internal versus external tocodynamometry for monitoring labor showed no difference in rates of operative delivery or fetal outcomes between the two groups. Internal tocodynamometry is more costly and more invasive and thus should be reserved for specific circumstances (see Indications). [2, 3]
Indications
An intrauterine pressure catheter is placed when quantification of contraction strength is desired, typically to assess the adequacy of spontaneous contractions in cases of arrested cervical dilation.
It may also be used to facilitate titration of the oxytocin dosage during induction or augmentation of labor. Placement of an intrauterine pressure catheter can reduce the use of oxytocin during high-risk labor with signs of fetal distress. [4]
An intrauterine pressure catheter can provide a more accurate assessment of contraction duration, length, and strength in patients in whom external tocodynamometry does not pick up contractions well, such as in obese patients.
In cases of fetal heart rate decelerations, an intrauterine pressure catheter can be used to clarify the relationship between the timing of the deceleration and the contraction.
Finally, intrauterine pressure catheter placement also allows an amnioinfusion to be performed in cases of severe variable fetal heart rate decelerations.
Contraindications
An intact fetal membrane is a contraindication to intrauterine pressure catheter placement, as the desired location is within the amniotic space. Amniotomy just prior to intrauterine pressure catheter placement is acceptable in the absence of contraindications to amniotomy.
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IUPC tracing
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An intrauterine pressure catheter and cable.
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An example of a fetal heart rate and contraction monitor.
