EXTERNAL DEVICES
External devices (most common) are placed on the uterine fundus. Advantages
are utilization before significant cervical dilation and membrane rupture.
Disadvantages are poor quality tracing with maternal obesity and maternal
discomfort from the device belts.
Fetal. A continuous ultrasound transducer picks up fetal cardiac motion but
also can register maternal great vessel pulsations.
Contractions. A tocographic transducer device senses the change in uterine
wall muscle tone. It can measure the beginning and ending of contractions but
cannot assess contraction intensity.