Fetal response to sound stimulation: preliminary report exploring use of sound stimulation in routine obstetrical ultrasound examinations.

An artificial larynx was used to sound-stimulate 693 human fetuses with gestational age ranging from 21 to 42 weeks. Fetuses were monitored, with simultaneous ultrasound, for immediate, increased motor activity after the stimulus. Each was scored as either demonstrating for startle response or having no visible response to the stimulus. Four zones of gestational development were determined: nonstartle zone (gestation age below 24 weeks), in which none reacted; transitional zone A (24 to 27 weeks), in which 30% reacted, transitional zone B (27 to 30 weeks), in which 86% reacted; and startle zone (above 31 weeks), in which 96% reacted. A review of the 17 patients not responding to sound in the startle zone, revealed a wide spectrum of complications of pregnancy in eight, including sepsis, meconium aspiration, short umbilical cord, abruption of the placenta, bradycardia, and death, while nine were without recorded abnormalities. Sound stimulation designed to elicit a startle response on ultrasound may have some potential benefit in identifying fetuses at risk or needing closer physiologic evaluation. Adding sound stimulation to the routine ultrasound study may warrant further study.