Zhang's guidelines vs WHO guidelines for diagnosing labour dystocia

We read with interest the Labour Progression Study (LaPS) by Stine Bernitz and colleagues1, which reported no differences between Zhang's guidelines and WHO guidelines for diagnosing labour dystocia.

Since diagnostic criteria only affect progression of labour by subsequent interventions, knowledge of to what extent the diagnosis of labour dystocia was followed by interventions is important. The protocol indicates that if labour dystocia is diagnosed according to either of the two guidelines, amniotomy would be performed followed by oxytocin. However, criteria for diagnosing failure to progress in labour, and the indications for intrapartum caesarean section (the primary outcome), are not sufficiently described.