The effect of fetal acoustic stimulation on fetal swallowing and amniotic fluid index.

OBJECTIVE

To determine the effect of fetal acoustic stimulation on fetal swallowing and amniotic fluid (AF) index in an attempt to understand the potential mechanism for fetal compromise following fetal acoustic stimulation.

METHODS

Fetal swallowing movements and AF index were assessed in 90 full-term fetuses before and after fetal acoustic stimulation. Fetal swallowing movements were identified on a video monitor and measured in terms of the percentage of time they occurred during 30 minutes of observation. The fetal heart rate was recorded 30 minutes before and 30 minutes after fetal acoustic stimulation.

RESULTS

The mean (+/- standard deviation) percentage of time spent by the fetus in swallowing increased from 16.1 +/- 6% before to 44.3 +/- 10.3% after stimulation (P < .005). The AF index decreased from 14.6 +/- 8.4 cm before acoustic stimulation to 12.8 +/- 6.8 cm afterward (not statistically significant). Seven of 17 patients (41%) with borderline AF indexes developed oligohydramnios after the fetal acoustic stimulation; two of these demonstrated persistent variable decelerations that required obstetric intervention.

CONCLUSIONS

Fetal acoustic stimulation is associated with increased fetal swallowing activity, which can lead to diminution of AF volume. The AF index should be assessed in fetuses before acoustic stimulation and if the volume is low, acoustic stimulation should be used with extreme caution.