Data collection
Two qualified nurses obtained all data. Clinical characteristics included maternal age, height, weight, body mass index (BMI), parity, gestational age (GA), and haemoglobin concentration. The SI was defined as the ratio of HR to SBP.23 to measure HR and SBP, which was measured using a digital calibrated sphygmomanometer (Omron M6 Comfort, OMRON Healthcare, Kyoto, Japan). For all cases, at least seven measures of the SI were obtained: 1) at the active phase of the first stage of labour, 2) during the second stage of labour, 3) within 15 min postpartum, and 3) every 30 minutes until two hours postpartum (four measures). All SI values were masked by the treating clinicians and used only for research purposes. Based on the World Health Organization criteria, maternal anaemia was defined as less than or equal to 11 g/L.24 The presence of PPH as registered on the clinical charts was also recorded. All patients were followed up until their discharge.