The conundrum of vanishing early decelerations in British obstetrics, a step backwards? Detailed appraisal of British and American classifications of fetal heart rate decelerations - fallacies of emphasis on waveform and putative aetiology.

A recent opinion survey of British Obstetricians revealed 'early' fetal heart rate (FHR) decelerations as the commonest type in their practice. This contrasts with the guidelines by the National Institute for Health and Clinical Excellence, UK (NICE 2007) that 'true uniform early decelerations are rare and most decelerations are variable'. This analytical review suggests that the emphasis on putative aetiology and 'waveform' of decelerations by NICE and other national guidelines leads to fundamental inconsistencies. 'Uniform shape' is misinterpretation of the description by Hon and Quilligan (1968). Truly 'uniform' (identical)) decelerations do not occur and no examples can be found. Gradual ('bell') or rapid shape has no correlation to putative causation or fetal condition. Obstetricians and midwives should seek clarification of these fallacies. The previous British practice of classifying decelerations based solely on time relationship to contractions seems most scientifically robust leading to more consistent interpretation and better discrimination of fetal status.