Preterm and term fetal cardiac and movement responses to vibratory acoustic stimulation

To assess fetal response to vibratory acoustic stimulation, 24 preterm (group A; <36 weeks' gestation) and 30 term (group B; ≥36 weeks' gestation) pregnancies were studied. Study variables were perceived fetal movement, fetal heart rate, and fetal heart rate pattern. Observer- and patient-perceived fetal movement responses were noted in most cases but were slightly more common in term patients (group A: +fetal movement, patient 87.5%/observer 87.5%) group B: +fetal movement, patient 96.7%/observer 90%). Baseline changes in fetal heart rate (≥10 beats/min) were observed in 46% of preterm fetuses and 70% of term fetuses. Tachycardia (fetal heart rate >160 beats/min) was a common finding in both groups. In group A, tachycardia after vibratory acoustic stimulation persisted more than 1 minute in 29.2% and more than 5 minutes in 12.5% of patients. In group B tachycardia beyond 1 and 5 minutes was noted in 73.3% and 50% of patients, respectively. A significant shift to "awake" fetal heart rate patterns occurred in both groups; 29% to 79% was noted in group A (p < 0.001) and 46.7% to 90% in group B (p < 0.001). When vibratory acoustic stimulation was used, the high occurrence of increased baseline, tachycardia, and emergence of unusual fetal heart rate patterns must be recognized to adequately interpret fetal heart rate tracings.