Safety Spotlight: Investigations into equipment and technology used for continuous fetal heart rate monitoring

A baby's heart rate was being monitored with a CTG abdominal transducer. The mother's heart rate was also being monitored using a finger probe pulse oximeter, attached to the CTG machine. The mother and baby’s heart rates were displayed visually on the CTG machine and recorded on the CTG trace. It was likely that the abdominal transducer lost contact with the baby’s heart rate and recorded the mother’s heart rate as shown on the CTG trace below.

The average calculation time of the maternal pulse from a CTG’s pulse oximeter finger probe can be different to the maternal pulse recorded by an abdominal transducer. This can lead to a delay in the calculation and the recording of the mother’s heart rate, in this example, of up to 12 seconds. This meant that there were two different values being shown on the CTG visual display and this reassured staff that there were two different heart rates being heard, when it was likely to be the mother’s heart rate on both. To prevent a mother’s heart rate being inadvertently interpreted as a baby’s heart rate it is worth considering the following questions:

• Does your training include functionality of the CTG machines used in your Trust including how the machines work and alarm functions?
• Does the manufacturer’s guidance indicate a delay in the calculation and recording of the maternal heart rate for the CTG machines used by your trust?

This was first published in the Stakeholder Bulletin: March 2025 - Edition