Fetal response to external mechanical stimuli.

Several authors have recommended [1, 3, 8, 12] that the fetus be mechanically stimulated if the abdominal pregnancy CTG shows no accelerations. One expects the fetus to show a motor response to mechanical stimulation. Fetal movements expressed as accelerations in the abdominal CTG are considered to reflect "arousal" of the previously asleep fetus and are thought to be normal. An absence of such a response in considered by some as a sign of pathological fetal changes [3, 8, 12]. Others, however, have found that the normal non-stressed fetus need not change its sleep-arousal state after mechanical stimulation [5, 14]. An attempt was made to clarify this in the present work. We studied the CTG recordings and the ultrasound pictures in 63 pregnancies in a total of 83 cases for an average of 56 minutes. Fetal movements were marked by pressing a lever on the labor pressure chart. The fetus was mechanically stimulated by shaking its head manually for 5 seconds. Control recordings were also made, when the fetus was not so stimulated. The following results were obtained: With a normal CTG (reactive nonstress test, FISCHER score 8-10 points) Mechanical stimulation led to no changes in 87% of NREM sleep and in 93.9% of REM sleep. A change to a more active state (REM sleep + arousal) due to stimulation was found in 13% of NREM sleep, which is significantly more frequent than the 2.9% found when no stimulation occurred. A change from REM sleep to arousal was found in 6.1%, not significantly different from 1.8% found without stimulation. Short-lasting reactions to mechanical stimulation included movements, acceleration of fetal heart rate and dip 0. These reactions were equally frequent in REM and NREM sleep, i.e. 75% and 68.5% respectively. These reactions occurred by chance less frequently, in 14.5% of cases in REM and in 3% of cases in NREM sleep (Tab. II). The occurrence is significantly higher in REM than in NREM sleep. In a pathological CTG (Fischer score 7 points or less) our technique does not permit us to distinguish the different sleep-arousal states. Only the short-lasting response to mechanical stimulation of the fetus was hence evaluated. Mechanical stimulation resulted in a fetal response in 19% with decelerations of variable expression (Figs. 1a, 1b, 2, 3) similar to the variable decelerations observed during labor. These decelerations occurred only together with other signs of fetal distress in the CTG.(ABSTRACT TRUNCATED AT 400 WORDS)