The scalp stimulation test: a clinical alternative to fetal scalp blood sampling

Intrapartum fetal heart rate response to various scalp stimuli and its correlation with scalp pH was studied in a prospective manner. One hundred fetuses with heart rate tracings judged by the resident responsible for the patient to be suggestive of fetal asphyxia were entered into the study. Each fetus was subjected to firm digital pressure on the head followed by a gentle pinch of the scalp with an atraumatic clamp. Scalp blood sampling was then performed in the usual manner. Response to either of these stimuli by an acceleration of the fetal heart rate of 15 bpm lasting at least 15 seconds was uniformly associated with a scalp blood pH of greater than or equal to 7.19. Fifty-one fetuses so stimulated responded with an acceleration. Of the remaining fetuses, 19 had a scalp pH less than 7.19 and 30 were associated with a pH greater than 7.19. Clinical application of such a scalp stimulation test could, therefore, reduce the necessity for scalp blood sampling by approximately 50% in the presence of a fetal heart rate pattern suggesting acidosis. Such a provocative test may also be very useful with an abnormal fetal heart rate pattern suggestive of acidosis when the cervix is sufficiently dilated to permit scalp blood sampling.