2.3 Study variables
Primary PPH was defined as maternal blood loss ≥ 500ml within 24 hours after birth. The data sources included the hospital’s clinical electronic database, electronic medical records and paper fluid order documentation. Maternal estimated blood loss (EBL) was extracted from the hospital’s clinical electronic database. In cases where EBL was missing from the clinical electronic database, case documentation was reviewed by the lead author to identify the clinician recorded EBL within the written electronic progress notes. The total volume of IV fluids administered was determined by reviewing related documentation within the clinical electronic database, electronic medical records, and paper fluid order documentation. The total volume of IV fluids administered was calculated from the point of first administration during labour to the time of birth. While the complete medical records (electronic and paper fluid order documentation) consistently recorded the total number of bags of fluids prescribed, it was often unclear what proportion of the final bag of fluids had been administered before the time of birth due to unreliable documentation of IV fluid administration rates in the electronic clinical records. Total intrapartum IV fluid volume was therefore manually estimated by determining the duration of time over which the previous bag of fluids was administered, calculating the rate (in mL/hr), and applying this rate to the final bag. In cases where a single bag of IV fluids was administered, the rate could not be determined, and it was assumed that the total bag volume (including the additional volume of any oxytocin) was administered by time of birth.
Secondary outcomes included: Severe primary PPH (defined as maternal blood loss ≥ 1000 mL within 24 hours after birth); atonic PPH; immediate PPH management; blood product transfusion; major perineal injury (≥ 3rd degree perineal injury); and caesarean section birth. Additionally, variables were collected as co-variates, these included: birth weight; maternal pyrexia (≥ 38 °C on at least one occasion during labour); intrapartum IV antibiotics for infection; duration of active labour (from the time of regular uterine contractions with the cervix ≥ 4cm dilated to the time of birth); epidural anaesthesia during labour; instrumental birth; emergency caesarean section; genital tract injury; retained placenta/membranes; hypertensive disorders of pregnancy; model of care; body mass index (BMI); and parity. Baseline characteristics and demographic variables were collected in accordance with the Core Outcomes in Women’s and Newborn Health (CROWN) initiative.(18)