Uterine/Fetal Monitors

There are a number of fetal and uterine monitors of varying capabilities available for the antepartum (pre-labor) measurement of fetal activity. Some, like the SpaceLabs AM66 and the Hewlett Packard 8040, are all-inclusive devices which monitor uterine and fetal activity in the home and print out a graph of the activity using a printer directly on the face of the device. With an optional modem board, these models can also transmit the data to a central receiving station via the phone line. Uterine activity and fetal heart rate is monitored externally (with an option for internal monitoring) using a ultrasound tocotransducer strapped to the abdomen of the patient. This tocotransducer sends sound waves into the maternal abdomen and detects echoes coming from moving objects within. The monitor analyzes these echoes, picking out indications of fetal heart motion, and uses the rhythm of the motions to compute heart rate. At the same time, the tocotransducer detects uterine activity by sensing changes in tension on the abdomen. In addition, the mother holds a marker cable, similar to a bolus cord, and presses the button whenever uterine activity is detected; this places a mark on the graph so that the heartbeat of the fetus and the uterine activity can be corrolated.

Some Uterine activity monitors such as the Homevue System provide network-based solutions to monitoring, allowing a large number of patients to feed data to a single central receiving station via modem connections.

Doppler fetal monitors, on the other hand, utilize the frequency of ultrasonic waves reflected from a moving surface (the fetus) and use the difference between this frequency and that of incident waves to calculate the fetal heartrate. These devices range from small hand-held units with headphones operating at low frequencies (approx. 3 MHz) with no memory or print capabilities, to sophisticated units which measure over a broad frequency range and provide activity history and printouts. Hand-held units available include the IMEX Pocket-Dop II and the SpaceLabs DOP-1.

Available Uterine/Fetal Monitors:

SpaceLabs AM66 (UXAM66)

SpaceLabs DT100B Transmitter, DR100 Receiver (UXDT100B, UXDR100)

Hewlett Packard 8040 (HP8040)

Imex Pocket DopII, SpaceLabs DOP-1 (IXDOP2, UXDOP)