Objective
Electronic fetal heart rate monitoring was developed to identify fetuses at risk of acidemia for intervention before adverse outcomes. Our objective was to compare the 3-tier system with a 5-tier system in evaluation of fetal acidemia.
Study Design
Retrospective case-control study of patients with a fetal arterial pH <7 matched to the next birth that resulted in a pH >7.2. Tracings were categorized into 3- and 5-tier systems by a single reviewer. Sensitivities and specificities were calculated for each.
Results
Twenty-four cases and 24 controls were identified. The sensitivity for an orange or red tracing was higher than for category III, with more of these in the pH <7 group compared with controls ( P ≤ .001). There were significantly more green, blue, and yellow tracings in the normal pH group compared with the pH <7 group ( P = .033, P = .008, P = .023), respectively.
Conclusion
The 5-tier system had a better sensitivity than the 3-tier system.
The use of intrapartum electronic fetal heart rate monitoring (EFM) is widespread, with 89% of singleton pregnancies monitored in 2004. However, despite previous attempts, developing a standardized approach to interpretation and management has been problematic. Although EFM is often criticized for having a high false-positive rate as it is unable to predict cerebral palsy, this is not the intended goal. EFM is used to detect patterns that reflect significant hypoxia and allow intervention before fetal injury. Initial studies demonstrated the significance of EFM in reducing intrapartum mortality and detecting fetal acidemia when compared with intermittent auscultation but also showed an increase in cesarean and operative vaginal deliveries. As EFM analysis has been limited by poor inter- and intraobserver variability, in 2008, the National Institute of Child Health and Human Development (NICHD) along with the Society for Maternal-Fetal Medicine (SMFM) and the American College of Obstetricians and Gynecologists (ACOG) convened a workshop to update definitions for fetal heart rate (FHR) tracings and assist in the interpretation and management. At this workshop, several EFM interpretation systems were reviewed, including the 1 by Parer and Ikeda, who constructed a grid of all possible fetal heart rate patterns and classified each into 1 of 5 categories using the color coding of the Homeland Security Advisory System—green = low risk, red = severe risk of academia, and/or evolution to a more serious pattern ( Table 1 ). At the conclusion of the workshop, attendees agreed on a 3-tier interpretation system, which is currently recommended for use in intrapartum fetal assessment ( Table 2 ).
| Variable | |
| Green: | Orange: |
| Normal baseline | If moderate variability: |
| Moderate variability | -Tachycardia with severe VD, LD, or PD |
| ± early or mild VD | -Normal baseline with severe PD |
| Blue: | -Mild bradycardia with severe VD, LD. or PD |
| If moderate variability: | -Moderate bradycardia with severe VD, LD, or PD |
| -Tachycardia with early or mild VD | -Any severe bradycardia |
| -Normal baseline with moderate VD or mild LD | If minimal variability: |
| If minimal variability: | -Tachycardia with moderate/severe VD, mild/moderate LD, or PD |
| -Tachycardia without decelerations | -Normal baseline with moderate/severe VD, mild/moderate LD, or PD |
| -Normal baseline ± early decelerations | -Mild or moderate bradycardia ± early deceleration |
| Yellow: | If absent variability: |
| If moderate variability: | -Normal baseline |
| -Tachycardia with moderate VD, mild/moderate LD, or PD | Red: |
| -Normal baseline with severe VD, moderate/severe LD, mild/moderate PD | If minimal variability: |
| -Mild bradycardia ± early, mild/moderate VD, LD, or PD | -Tachycardia with severe LD |
| -Moderate bradycardia ± early decelerations | -Normal baseline with severe LD or PD |
| If minimal variability: | -Mild or moderate or severe bradycardia with any VD, LD, or PD |
| -Tachycardia with early or mild VD | If absent variability: |
| -Normal baseline with mild VD | -Any baseline with any deceleration |
| Marked variability | Sinusoidal |
| Category |
| Category I: |
| Baseline rate: 110-160 beats per minute |
| Baseline variability: moderate |
| Late or variable decelerations: absent |
| Early decelerations: present or absent |
| Accelerations: present or absent |
| Category II: |
| Includes all tracings not categorized as Category I or III |
| Category III: |
| Absent baseline FHR variability and any of the following: |
| -Recurrent late decelerations |
| -Recurrent variable decelerations |
| -Bradycardia |
| Sinusoidal pattern |
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