Fetal blood sampling (FBS) pH in labour

The classification of fetal blood sample (FBS) results pH

• pH >=7.25 Normal
• pH 7.21-7.24 Borderline
• pH < = 7.20 Abnormal
  • results should be interpreted taking into account the previous pH measurement, the rate of progress in labour and the clinical features of the woman and baby
  • after an abnormal FBS result, consultant obstetric advice should be sought
  • after a normal FBS result, sampling should be repeated no more than 1 hour later if the FHR trace remains pathological, or sooner if there are further abnormalities
  • after a borderline FBS result, sampling should be repeated no more than 30 minutes later if the FHR trace remains pathological or sooner if there are further abnormalities
  • the time taken to take a fetal blood sample needs to be considered when planning repeat samples
  • if the FHR trace remains unchanged and the FBS result is stable after the second test, a third/further sample may be deferred unless additional abnormalities develop on the trace
  • where a third FBS is considered necessary, consultant obstetric opinion should be sought
  • contraindications to FBS include:
    • maternal infection (for example, HIV, hepatitis viruses and herpes simplex virus)
    • fetal bleeding disorders (for example, haemophilia)
    • prematurity (less than 34 weeks).

Reference:

1. NICE (September 2007).Intrapartum care.