History

   However, in 1968, Benson et al. published results of a review of 24,863 labors in which IA was used throughout the 1950s. Fetuses were monitored every 15 minutes during the first stage of labor, and every 5 minutes during the second stage of labor. Their results concluded that IA was not a “reliable … indicator of fetal distress” except in the extreme situation of terminal bradycardia. This damning report emerged at a time when true electronic fetal monitoring (EFM) was being developed and experts were quick to dismiss IA in favor of the hoped-for promise of EFM.

Electronic Fetal Monitoring

   In 1906 Cremer described the use of the fetal electrocardiogram using abdominal and intravaginal electrical leads. That led other investigators to attempt to determine fetal status using electrocardiographic patterns only to conclude that fetal distress did not yield any consistent electrocardiographic patterns. Electronic fetal phonocardiography had been described originally by Henly in 1931. These devices simply used a microphone to magnify the auscultated FHR. In 1958, Hon, the pioneer of modern EFM, first described a system for capturing continuously the fetal ECG. In 1964, Callagan described a commercially viable system for capturing the FHR with Doppler technology. In the 1960s, EFM systems were made commercially available by Hon in the United States (1968); by Hammacher, a pioneer in the electronic systems to reduced noise-to-signal ratios, in Germany; and in Uruguay by Caldeyro-Barcia, father of among other things, Montevideo units and long-term and short-term variability. Hon had coined the terms early, late, and variable decelerations.

   The spiral electrode or fetal scalp electrode as used today was introduced by Hon in 1972. More complex electronic methods of differentiating between genuine fetal signal and artifact were introduced over time to work in tandem with Doppler technology, giving rise to modern electronic autocorrelation. By 1975, just over twenty percent of labors were monitored with EFM, a number that now stands at well over eighty percent.

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