Procedure
The intrapartum CTGs were interpreted by the patient’s midwife and the physician on call. When indicated, FBS was performed by the standard procedure described by Saling (15). For clinical decision making, the scalp blood was primarily analysed by LP, except at Sahlgrenska University Hospital where LP and/or pH was analysed (pH analysed by Stat-Profile-Prime-Analyzer, Nova Biomedical, Waltham, US). Simultaneously, from the same blood drop, the lactate level was measured by SSLX. The StatstripLactate®/StatstripXpress® meters are equally calibrated, approved by U.S Food and Drug Administration (FDA) and certified by the International Organization for Standardization (ISO). If the blood drop was too small for both tests, analysing of only LP or pH was performed. The sampling time and results were noted in the medical record. If FBS was repeatedly assessed from the same fetus, only the last value was entered into the database. The cut-offs for LP and pH employed; lactate level < 4.2mmol/L = normal, 4.2-4.8mmol/L = pre-acidaemia, and >4.8mmol/L = acidaemia and pH ≥7.20 = normal, and <7.20 = acidaemia. The clinical guidelines recommend repeated FBS within 20-30 minutes if values are pre-acidotic or if the CTG still is suspicious or pathological. Expedited delivery was recommended with an acidotic result (16,17). Paired umbilical cord blood was taken from all new-borns on unclamped cord directly after delivery in pre-heparinized syringes and analysed within fifteen minutes by stationary blood gas analysers (BGA) in the labour units (ABL800, Radiometer, Copenhagen, Denmark or Stat-Profile-Prime Analyzer). For both BGAs the Base Deficit was calculated in extracellular fluid (BDecf).
Obstetric and neonatal outcome variables were retrieved from the electronic medical records (Obstetrix, Cerner) and entered retrospectively into the database. The entries from the medical records were checked by two different interpreters for every 50th recording.