title: The reliability of foetal blood sampling as a test of foetal acidosis in labour.
abstract: OBJECTIVE
  To establish whether foetal blood sampling for pH is a reliable test of foetal acidosis in labour by comparing paired foetal blood samples taken at a single procedure.
  
  
  METHODS
  We conducted a prospective study assessing 293 consecutive attempts at foetal blood sampling in labour over a four month period from February to May 2012. A total of 100 paired samples were suitable for analysis. We compared the consistency of pH results of paired foetal blood samples, evaluated cases where inconsistent results would result in conflicting clinical decisions, and explored factors associated with discordant results.
  
  
  RESULTS
  There was a statistically significant difference between the mean pH of the two samples: 7.297 (SD 0.065) versus 7.315 (SD 0.059), p<0.0005. Of the 100 paired samples, 43 had a difference greater than the laboratory acceptable maximum analytical difference of 0.038. There was discordance between the samples in 16 cases with results crossing a decision threshold, and in 11 cases (69%) delivery was by emergency caesarean section. Inconsistent results were not associated with specific clinical factors and occurred more often with senior operators.
  
  
  CONCLUSIONS
  Foetal blood sampling is considered by many as the gold standard in assessing intrapartum foetal wellbeing. We have demonstrated inconsistency of paired foetal blood pH results which suggests that foetal blood sampling should not be considered infallible.
authors.affiliation: Academic Department of Obstetrics and Gynaecology, Coombe Women & Infants University Hospital & Trinity College, University of Dublin, Dublin 8, Ireland.
authors.forename: Yvonne M
authors.initials: YM
authors.lastname: O'Brien
authors.forename: Deirdre J
authors.initials: DJ
authors.lastname: Murphy
mesh_terms: D000138:Acidosis / Q000097:blood / Q000175:diagnosis / Q000196:embryology*; D002585:Cesarean Section / Q000009:adverse effects; D015331:Cohort Studies; D003422:Critical Care; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D005323:Fetal Monitoring / Q000379:methods*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016555:Matched-Pair Analysis; D007744:Obstetric Labor Complications / Q000097:blood / Q000175:diagnosis*; D011247:Pregnancy; D011361:Professional Competence; D011446:Prospective Studies; D015203:Reproducibility of Results; D012535:Scalp / Q000098:blood supply* / Q000196:embryology