Current FHR monitoring: -
Limitations

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