Because the rate of false-positive diagnosis of EFM is high, attempts have been made to find ancillary tests that help confirm a nonreassuring FHR tracing.
In the case of an EFM tracing with decreased or absent variability without spontaneous accelerations, an effort should be made to elicit one. Four techniques are avail-able to stimulate the fetus: 1) fetal scalp sampling,
Allis clamp scalp stimulation, 3) vibro-acoustic stim-ulation, and 4) digital scalp stimulation. Each of thesetechniques involves accessing the fetal scalp through the di-lated cervix. In vibroacoustic stimulation, the fetal scalp isstimulated with a vibratory device, and in digital scalp stimulation, the physician uses his or her finger to gently stroke the scalp.
Each of these tests is a reliable method to exclude aci-dosis if accelerations are noted after stimulation. Because vibroacoustic stimulation and scalp stimulation are less in-vasive than the other two methods, they are the preferred methods. When there is an acceleration following stimu-lation, acidosis is unlikely and labor can continue.
When a nonreassuring FHR tracing persists without spon-taneous or stimulated accelerations, a scalp blood sample for the determination of pH or lactate can be considered (Fig. 9.12). However, the use of scalp pH has decreased, and it may not be available at some tertiary hospitals. Furthermore, the positive predictive value of a low scalp pH to identify a newborn with HIE is only 3%.
The use of pulse oximetry has been suggested as a modality to reduce the false-positive diagnosis of a non-reassuring FHR.
However, research has demonstrated that neither the overall rate of cesarean delivery nor the rate of umbilical arterial pH less than 7 decreased when pulse oximetry was used in association with EFM in cases of nonreassuring fetal status. Because of the uncertain ben-efit of pulse oximetry and concerns about falsely reassuring fetal oxygenation, use of the fetal pulse oximeter in clinical practice cannot be supported at this time. Additional stud-ies to test the efficacy and safety of fetal pulse oximetry are underway.