Current FHR monitoring: -
Limitations

Image showing the current technique of fetal heart rates

The current technique for recording fetal heart rate and uterine activity during pregnancy and L&D is to use Doppler Ultrasound and an external guard ring tocodynamometer. Although used throughout the world for over 30 years such systems present the following disadvantages:

  • Requires intermittent repositioning of the transducer and belt adjustments which is especially difficult on small and very large women.
  • Only suitable for use with trained users
  • The ultrasound and TOCO transducers are cumbersome, uncomfortable, and severely restrict movement.  A common problem is that belting often causes redness, itching and blisters. This can also occur under the sensing button on some TOCO transducers.
  • The technique involves insonating the fetus with a high frequency sound which is potentially harmful - see Current FHR monitoring Ultrasound safety.
  • On occasions the technique will not follow the fetal heart rate or uterine activity due to:
    • maternal heart rate pickup
    • Poor signal quality (fetal/transducer movement, belt tension, obesity, difficult presentation) resulting in missed beats, heart rate doubling/halving, missed contractions and other errors.
  • Monitoring large women is difficult
  • The FHR 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 unsupervised continuous long term monitoring