Ancillary tests

1. Fetal scalp stimulation. Fetal scalp stimulation is similar to the vibroacoustic stimulation test used antepartum. Absence of acidosis (ie, fetal pH greater than 7.20) is confirmed by elicitation of a FHR acceleration when an examiner stimulates the fetal vertex with the examining finger.

Fetal scalp sampling is recommended to further evaluate positive test results. 2. Fetal scalp blood sampling. Capillary blood collected from the fetal scalp typically has a pH lower than arterial blood. A pH of 7.20 was initially thought to represent the critical value for identifying serious fetal stress and an increase in the incidence of low Apgar scores. The degree of technical skill required prohibits widespread use of this modality.

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