Intrapartum vibratory acoustic stimulation of the human fetus during episodes of decreased heart rate variability

Vibroacoustic and scalp stimulation

Both VAS and scalp stimulation are useful in the evaluation of fetal compromise by decreasing the number of falsely abnormal FHR tests and limiting the number of unnecessary interventions, thus improving the efficiency of antepartum and intrapartum FHR monitoring. As is true for all types of fetal assessment using FHR monitoring, VAS and scalp stimulation have limitations, and a lack of response to these methodologies does not necessarily indicate fetal acidemia. When either VAS or scalp stimulation is employed, one must take into consideration their respective predictive values (see Table 1). Fetal VAS or scalp stimulation should be considered as one facet of comprehensive fetal evaluation. When these techniques are used in this manner, the clinician evaluating the fetus in the antepartum or intrapartum period may prevent unnecessary intervention and improve maternal and neonatal outcome.

Antepartum vibroacoustic stimulation in patients with low fetal heart rate variability

OBJECTIVE

The purpose of this study was to examine the effect of vibroacoustic stimulation during low fetal heart rate (FHR) variability.

METHODS

FHR was analyzed 30 min before and 30 min after computerized vibroacoustic stimulation using the Oxford Sonicaid system 8000. The study comprised 32 healthy pregnant women with low antepartum FHR variability. The significance of difference of the median values was examined using Wilcoxon's matched-pairs signed-ranks test.

RESULTS

Vibroacoustic stimulation of the fetus during low FHR variability evoked a significant increase in the number of accelerations (> 10 bpm) and an increase in long- and short-term variation.

CONCLUSION

Our findings indicate that vibroacoustic stimulation during low FHR variability produces an abrupt change from a quiet to an active fetal state.

An evaluation of antenatal fetal acoustic stimulation

Fetal heart rate reactivity was evaluated following acoustic stimulation testing (AST). The AST and NST (non-stress test) were compared with regards to certain adverse perinatal outcome criteria, and in a selected sample of cases, to other surveillance tests. These tests were the oxytocin challenge test (OCT) and biophysical profile (BPP). 479 tests were performed on 240 high-risk patients. The AST significantly increased fetal heart rate reactivity. With regards adverse perinatal outcome criteria, there was no significant difference between the AST and NST in relation to sensitivity, specificity or predictive values. In the 38 patients with both non-reactive NSTs and reactive ASTs, 5 (13.5%) had immediate follow-up surveillance tests (OCTs and/or BPPs) that were non-reassuring and necessitated delivery. In four of the five cases, there was evidence of potential fetal compromise. These preliminary observations suggest that the AST may have evoked reactivity in fetuses with early compromise, and raise concerns about replacing the NST with the AST as a primary screening test of fetal well-being.

Vibroacoustic stimulation and fetal heart rate in nonstress tests

Two methods of vibroacoustic stimulation were compared with traditional nonstress tests. Fetal heart rate tracings following stimulation had more accelerations and were of greater amplitude and duration than in the control group. The length of time required to obtain a reactive nonstress test was almost 15 minutes shorter when vibroacoustic stimulation was applied than when vibroacoustic stimulation was not used. Vibroacoustic stimulation elicited a heightened reactivity that persisted beyond the observation period in 30 of 45 (67%) of the experimental group subjects.

Fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition

Fetal acoustic stimulation has recently received much attention in the literature. This study evaluates fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition. The study group consisted of 201 patients, approximately 60% of whom had complicated pregnancies. All were in the latent phase of labor with singleton, vertex-presenting fetuses. Gestational age ranged from 37 to 43 weeks. Fourteen of the 201 fetuses (7%) showed a nonreactive response to fetal acoustic stimulation and those fetuses were at significantly greater risk of initial and subsequent abnormal fetal heart rate patterns, meconium staining, and cesarean delivery because of fetal distress and Apgar scores less than 7 at both 1 and 5 minutes. Transient fetal heart rate decelerations after a reactive response occurred in 25% of patients; however, fetal outcome was not worse in this group. A reactive response to fetal acoustic stimulation was associated with high specificity and negative predictive values. Therefore we conclude that fetal acoustic stimulation in the early intraprtum period may discriminate the compromised from the noncompromised fetus.

An overview of vibroacoustic stimulation

Vibroacoustic stimulation of the fetus as a test of fetal well-being has become fairly common despite limited research on this tool. A review of the literature reveals that fetal accelerations in response to this stimulus are indicative of fetal health. Vibroacoustic stimulation correlates well with other methods of fetal assessment and is effective in converting nonreactive tracings to reactive tracings in healthy fetuses, saving patients time and expense.