Intrapartum assessment of fetal well-being: A comparison of scalp stimulation with scalp blood pH sampling

Objective: To determine whether the need for fetal scalp pH sampling is decreased by the scalp stimulation test and whether redefinition of reactivity and presence of variability further decrease the need for scalp pH sampling. Methods: One hundred eight women with fetal heart rate (FHR) patterns suggestive of acidosis underwent fetal scalp blood pH evaluations. Digital scalp stimulation was performed for 15 seconds 1-2 minutes before pH sampling. The study group was subdivided based on reactivity to scalp stimulation and scalp puncture and was correlated with pH values. Reactivity was defined as an acceleration of 15 beats per minute or more lasting at least 15 seconds and redefined as an acceleration of 10 beats per minute or more lasting at least 10 seconds. Nonreactive responses were subdivided based on FHR variability preceding the scalp stimulation and were correlated with pH values. Fisher exact test was used for analysis. Results: All 51 instances of acceleration of 15 beats per minute or more lasting at least 15 seconds following scalp stimulation had a scalp pH of 7.20 or more. Using an acceleration of 10 beats per minute or more lasting at least 10 seconds, seven more reactive responses were obtained after scalp stimulation, all with pH of 7.20 or more. The 15 instances in which the pH was less than 7.20 were nonreactive irrespective of the definition of reactivity (P < .001). Twenty-one of the 50 instances of nonreactive responses (reactive response: acceleration of 10 beats per minute or more lasting at least 10 seconds) had positive variability. Only two of these 21 (9.5%) instances compared to 13 of the 29 (45%) instances with negative variability had pH less than 7.20 (P < .007). Conclusions: The scalp stimulation test could decrease the need for fetal scalp blood sampling by 47%. Redefinition of reactivity could decrease the need for scalp sampling by 54%. In addition, assessment of FHR variability before scalp stimulation could decrease further the need for scalp blood sampling by 73%. Copyright (C) 1997 by The American College of Obstetricians and Gynecologists.