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).
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