Vibroacoustic Stimulation of the Fetus Using a Conventional Mechanical Alarm Clock

> Objective: For more than 20 years, vibroacoustic stimulation testing (VAST) using an artificial larynx has been used worldwide when fetal heart rate monitoring produced patterns with absent or very low variability. In addition to the artificial larynx many other appliances have been used to stimulate a seemingly dormant fetus, but these have rarely been evaluated properly. In this study we tried to evaluate the use of standard mechanical wind-up alarm clocks for VAST. Methods: VAST with an alarm clock was performed successfully in 80 women with normal pregnancies from 36 weeks to term. It was tested by placing the alarm clock on the maternal abdomen just above the fetal head or on the controlateral side of the maternal abdomen to see whether position made any difference and whether coupling with ultrasound gel applied between the alarm clock and the maternal abdomen would affect the degree of fetal reaction to VAST as expressed in heart rate acceleration. Similarly, the effect of the alarm clock VAST on subjective and objective fetal movement patterns as registered by kineto-cardiotocotraphy (K-CTG) in addition to heart rate patterns was investigated. Results: All fetuses showed heart rate acceleration, an increase in heart variability, and increase in movement patterns in the 6 min after the application of alarm clock VAST. No statistically significant difference was found which would favor a particular placement of the alarm clock on the maternal abdomen or the use of ultrasound coupling gel. When K-CTG was performed, patient-perceived fetal movements as expressed with an event marker showed agreement with the machine-registered movements only when patients could see the tracing during registration and no accordance when the K-CTG was turned toward the wall during registation. Conclusion: In keeping with the ALARA principle a conventional wind-up alarm clock appears to be an inexpensive and effective alternative to the electrolarynx.