Reactive fetal heart rate response to vibroacoustic stimulation in fetuses with low scalp blood pH.

Fetal vibroacoustic stimulation in fetuses with suspicious or ominous fetal heart rate traces in labour was followed by acid-base balance determination on fetal scalp blood within 30 min of the test. The mean fetal scalp blood pH values were significantly higher in fetuses that showed reactive responses with fetal heart rate acceleration compared with those who had no response or responded with a deceleration to the vibroacoustic stimulation (pH 7.30 and 7.22 respectively). However, acidotic scalp blood pH values (7.16 and 7.18) were found in two fetuses which had shown reactive responses both to vibroacoustic stimulation and pain stimuli with scalp blood sampling.