The nonstress test is used to find out whether a fetus in the uterus is in fetal distress or not. The reliability of this nonstress test is very highly evaluated.
However, a pregnant woman has to lie down for a long period of time during the test. Therefore, the disadvantage of this test is that dorsal-position hypotension syndrome, unique to a pregnant woman, or fatigue may occur. In a number of cases, the burden imposed on the pregnant woman is quite significant.
In order to overcome this problem, this study was undertaken. Vibratory stimuli were given to a fetus in the uterus through the abdominal wall of a pregnant woman and the response of the fetus against these stimuli were recorded. Thus it was studied whether a result similar to the nonstress test may be accomplished during a short period of time or not. At the same time, the effect on the fetus was also studied. The sound volume was reduced as much as possible to a level whereby the response from the fetus could be clearly recorded.
The following results were obtained:
1) Among 250 Hz (85 dB), 50OHz (75 dB), 3, 000 Hz (70 dB), 5, 000 Hz (65 dB) and the supersonic Doppler fetal heart-beat sound (65 dB), the supersonic Doppler fetal heart-beat sound obtained the best response from the fetus, and also this heart-beat sound was the weakest as a form of stimulation. Thus, this heart-beat sound was the most distinguished from the viewpoint of practical use.
2) When comparing the vibratory stimuli inspection (based on the supersonic Doppler fetal heart-beat sound) with the nonstress test, the examples of "nonstress test : reactive" were often found in the examples of "vibratory stimuli inspection : positive." On the other hand, the examples of "nonstress test : nonreactive" were often found in the examples of "vibratory stimuli inspection: negative". So, it seems likely that the same degree of reliability can be found between these 2 inspections.
3) In the examples of "vibratory stimuli inspection (with supersonic Doppler fetal heartbeat sound) : negative", there existed many undesirable cases such as intrauterine growth retardation (light for dates), examples of declination of feto-placental functions, fetal distress and neonatal asphyxia. So, in terms of such occurrences, results found in the vibratory stimuli test were of the same degree as in the nonstress test.