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.