• cervical dilation;
  • length of labour


In the 1950s, Emanuel Friedman described the first comprehensive method of evaluating labour in clinical practice. In this landmark work, Friedman described the relationship between the duration of labour and cervical dilation as a sigmoid curve and outlined a tool for following labour progression and for identifying abnormal labour. His definitions of labour protraction and arrest continue to be applied in contemporary obstetric practice, although there have been considerable changes since in the clinical management of labour and delivery. This paper provides an overview of Friedman's work, addresses various methodological challenges in studying labour progression, and describes the utility of more advanced statistical methods for studying labour progression, such as survival analysis, compared with other approaches. Additional research that utilises and refines such methods will provide greater insight into labour progression and may assist in updating the diagnostic criteria for labour protraction and arrest disorders in contemporary obstetric practice. Moreover, such detailed information could have important clinical implications towards reducing the rate of primary caesarean delivery in the United States.