IS INTRAPARTUM VIBRATORY ACOUSTIC STIMULATION A VALID ALTERNATIVE TO FETAL SCALP PH DETERMINATION

Objectives To determine the association between fetal heart rate accel erations, whether spontaneous or induced by vibratory acoustic stimula tion, and subsequent scalp pH values in presence of a suspicious intra partum fetal heart rate tracing, and thereby assess the ability of acc elerations to predict a concurrent normal fetal scalp blood pH. Design Prospective observational study of 253 labours involving 421 pH sampl es. Setting Tertiary care university hospital of Geneva. Intervention Vibratory acoustic stimulation through the maternal abdominal wall for five seconds prior to fetal blood sampling. Main outcome measures Spo ntaneous fetal heart rate reactivity (accelerations) in the 10 min pre ceding vibratory acoustic stimulation, vibratory acoustic-induced reac tivity prior to fetal blood sampling, and scalp pH value. Results The positive predictive value of a reactive fetal heart rate response afte r vibratory acoustic stimulation was 78% (95% CI 73-84%) and 97% (95% CI 94-99%) for scalp pH values of > 7.25 and greater than or equal to 7.20, respectively. Similar observations occurred with spontaneous rea ctivity. Of concern, 7 out of 31 (23%) occasions where the scalp blood pH was less than 7.20 appeared to be associated with a normal fetal h eart rate response to vibratory acoustic stimulation. Conclusions Feta l heart rate acceleration induced by vibratory acoustic stimulation wa s significantly associated with a normal scalp blood pH higher than 7. 25. However, vibratory acoustic stimulation offers no advantage over o bservation of spontaneous fetal heart rate tracings and cannot safely replace fetal blood sampling during labour.