Clark and coworkers (1984) have suggested that fetal scalp stimulation is an alternative to scalp blood sampling. his proposal was based on the observation that heart rate acceleration in response to pinching the fetal scalp with an Allis clamp just before obtaining blood was invariably associated with a normal pH. Conversely, failure to provoke acceleration was not uniformly predictive of fetal acidemia. Later, Elimian and associates (1997) reported that of 58 cases in which the fetal heart rate accelerated > 10 bpm after 15 seconds of gentle digital stroking of the scalp, 100 percent had a scalp blood pH of > 7.20. Without an acceleration, however, only 30 percent had a scalp blood pH > 7.20. Following a prospective cohort study, Tahir Mahmood and coworkers (2017) concluded that fetal scalp stimulation was a reliable alternative to scalp blood pH determination.
Fetal heart rate acceleration in response to vibroacoustic stimulation has been recommended as a substitute for fetal scalp blood sampling (Edersheim, 1987). The technique uses an electronic artificial larynx placed approximately 1 cm from or directly onto the maternal abdomen (Chap. 17, p. 337). Response to vibroacoustic stimulation is considered normal if a fetal heart rate acceleration of at least 15 bpm for at least 15 seconds occurs within 15 seconds after the stimulation and with prolonged fetal movements (Sherer, 1994).
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FIGURE 24-23 Frequency distribution of umbilical artery oxygen saturation values in 1281 vigorous newborn infants. Dotted line indicates normal distribution. (Redrawn with permission from Arikan GM, Scholz HS, Petru E, et al: Cord blood oxygen saturation in vigorous infants at birth: what is normal? BJOG. 2000 Aug;l07(8):987-994.)
Lin and colleagues (2001) prospectively studied vibroacoustic stimulation in 113 women in labor with either moderateto-severe variable or late fetal heart rate decelerations. hey concluded that this technique is an efective predictor of fetal acidosis in the setting ofvariable decelerations. The predictability for fetal acidosis, however, is limited in the setting of late decelerations. Other investigators have reported that vibroacoustic stimulation in second-stage labor did not predict neonatal outcome or enhance labor management (Anyaegbunam, 1994).
Skupski and coworkers (2002) performed a metaanalysis of reports on intrapartum fetal stimulation tests published between 1966 and 2000. Four types of fetal stimulation were analyzed and included fetal scalp puncture for blood pH testing, llis clamp pinching of the fetal scalp, vibroacoustic stimulation, and digital strokingofthe fetal scalp. Results were similar for all four methods. These investigators concluded that intrapartum stimulation tests were useful to exclude fetal acidemia. They cautioned, however, that these tests are "less than perfect."