Evoked fetal startle response: a possible intrauterine neurological examination.

The fetal startle reflex was studied in an attempt to provide an objective and quantitative estimate of the fetal neurological condition. This reflex is a normal response to a combined sound-vibratory stimulus in the healthy infant born after 30 weeks of gestation. It consists of a generalized paroxysmal motion that involves the whole body. Thirty women with uncomplicated pregnancies, who subsequently delivered healthy infants, were studied at term. Fetal movements were monitored by means of a real-time scanner. Placement of the transducer was such that it allowed for visualization of the long axis of the fetal forearm. A 3-second stimulus was delivered on the maternal abdomen over the fetal head with use of an artificial larynx. This device generates a mixed sound-vibratory output of 100 dB and 85 Hz. Sufficient visualization of the plane of forearm motion was possible 68% of the time, thus allowing for measurement of the duration of this motion. The results indicate that the mean duration of forearm motion in response to a 3-second sound-vibratory stimulus is 8.2 +/- 2.3 seconds (+/- SEM). Since an immediate forearm motion was detected each time that a stimulus was applied, we conclude that the startle reflex does indeed exist in the fetus. This simple means of assessing the neurological state of the fetus may provide a way to evaluate fetal tone as it applies to antenatal fetal assessment.