Current FHR monitoring: -
Limitations

The current technique for recording fetal heart rate during pregnancy is to use Doppler Ultrasound. Although used throughout the world for 30 years such systems present the following disadvantages:

• Require intermittent repositioning of the transducer
• Only suitable for use with trained users
• The ultrasound and toco transducers are cumbersome and uncomfortable and often severely restricts movement
• The technique involves insonating the fetus with a high frequency signal which is potentially harmful - see below.
• On occasions the technique will not follow the fetal heart rate due to:
  • maternal heart rate pickup
  • rapid FHR changes
  • Poor signal quality (fetal/transducer movement, obesity, difficult presentation) resulting in missed beats, heart rate doubling, and other errors.
• Monitoring large women is difficult
• The signal processing technique (auto correlation) by design, results in an average heart rate and can never provide a true beat to beat number
• The technique cannot be used for routine continuous long term monitoring e.g. overnight to assess fetal behavior, or capture 'rare' but clinically relevant events.