Why was a new NICHD workshop on electronic fetal monitoring reconvened?
In the 1990s, the National Institute of Child Health and Human Development (NICHD) sponsored a series of workshops that culminated
in the publication of nomenclature, definitions, and guidelines for electronic fetal heart rate monitoring (EFM) in 1997.1 Since then, a number of organizations have produced new documents on EFM that have included different pattern interpretation
systems.2 In 2008, the American College of Obstetricians and Gynecologists (ACOG), the Eunice Kennedy Shriver National Institute of
Child Health and Human Development, and the Society for Maternal-Fetal Medicine co-sponsored a follow-up workshop on EFM with
the following goals: (1) review and update the definitions for fetal heart rate (FHR) patterns from the prior workshop, (2)
evaluate existing classification systems and make a recommendation for a system for use in the United States, and (3) set
research priorities for EFM.3 Our hope was that a revised classification system would allow for clearer communication between all members of the health-care
team.
How was the new classification system selected?
Table 1 Three-tier FHR interpretation system
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A classification system was felt to be essential and was the topic of much discussion during the workshop. First, we heard
detailed presentations from the Royal College of Obstetricians and Gynaecologists and from the Society of Obstetricians and
Gynecologists of Canada that focused on the process of development and components of their systems. Both are three-tier systems
in which tracings are categorized into one of three categories. We also heard a presentation from Dr. William Parer from the
University of California, San Francisco. His group has developed and implemented a five-tier system for EFM interpretation.
The NICHD group was most interested in a simple system that would improve communication among clinicians. With that in mind,
we decided on a three-tier system for categorization (Table 1). Naming the categories was a surprisingly difficult task, but
ultimately we settled on three simple categories:
- CATEGORY I FHR tracings are normal
- CATEGORY II FHR tracings are indeterminate
- CATEGORY III FHR tracings are abnormal
We did recognize that many EFM tracings are Category II and that tracings can change back and forth between categories over
time.
How have definitions and nomenclature changed?
The new definitions are similar to the older ones in many respects. We reaffirmed the previous definitions for baseline FHR,
FHR variability, accelerations, and decelerations. It's important to stress that there is no distinction between long-term and short-term variability—variability should be assessed as a single unit.
One difference is in the nomenclature for uterine contractions. In the past, many terms were used for frequent contractions,
including tachysystole, hyperstimulation, hypertonus, and hypercontractility. That was confusing and fostered miscommunication.
The guideline recommended new nomenclature for uterine contractions as follows.
Contractions are quantified as the number present in a 10-minute window, but averaged over 30 minutes.
NORMAL: Five or fewer contractions in 10 minutes, averaged over 30 minutes.
TACHYSYSTOLE: More than five contractions in 10 minutes, averaged over 30 minutes.
Tachysystole should be further qualified as to the presence or absence of associated FHR decelerations. With this new system,
terms like hyperstimulation and hypercontractility should be abandoned.
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